(covers information from several alternate timelines)
As of the mid-2150s, the number of Denobulan inhabitants on their homeworld totaled twelve billion, all of whom shared one continent. (ENT: "The Catwalk") Consequently, living space was at a premium, and Denobulan culture had come to embrace close, communal lifestyles, though this habitation arrangement was due to choice, rather than necessity. (ENT: "Doctor's Orders")
As Phlox once admitted, family relations on Denobula could be extremely complicated. (ENT: "Terra Prime") Unlike Klingons, Denobulans didn't group themselves into Houses. (ENT: "Divergence") They typically preferred to be among large groups and found solitude uncomfortable. However, Denobulans - at least male Denobulans - were uncomfortable being touched by persons they were not intimate with. Denobulans were typically polyamorous, where a man typically had three wives, who each had three husbands. This created extremely large extended families.
In addition, Denobulan marriages were not exclusive, and married Denobulans could be intimate with anyone they chose. The females emitted powerful pheromones during their mating season. Male Denobulans often became combative during this time, and mating could require medical supervision. (ENT: "Dear Doctor", "A Night in Sickbay") Denobulan males were more inhibited than Denobulan women, and often found the idea of disrobing in front of others uncomfortable. (ENT: "Bounty") A typical romantic overture for a female Denobulan to give would be to offer their prospective mate a rose petal bath. (ENT: "Stigma") Doctor Jeremy Lucas once observed that, given the comparatively elaborate complexities of the Denobulans' mating cycle, they made Humans seem "like single-cell organisms." (ENT: "Dear Doctor") In Phlox's opinion, however, "Any man would be a fool to ignore the romantic overtures of a healthy Denobulan woman." (ENT: "Stigma") He also highly valued the complexity of Denobulan mating practices, being of the opinion that two people were insufficient for a "proper" Denobulan marriage, though a Denobulan woman could feasibly marry only a single Denobulan man. (ENT: "Divergence", "Doctor's Orders", "Stigma") A Denobulan woman who had only a single Denobulan husband could take his name as her surname. (ENT: "Stigma")
A traditional greeting for Denobulan lovers began with approaching each other face-to-face, so that each individual was not quite touching the other. The Denobulans then smelled the other's scent and finally parted. (ENT: "Stigma")
Denobulans were renowned for having an abundance of patience. This extreme patience could reflect on their marital interactions, so that they were quite content to spend a considerable length of time apart. (ENT: "Stigma")
Denobulans did not have conversations with each other while eating together, as they considered it a waste of time. (ENT: "Fight or Flight") Denobulans generally ate meat, including Denobulan sausage. (ENT: "A Night in Sickbay", "The Seventh") They invested much effort in hunting Denobulan lemurs, as a Denobulan delicacy was the kidneys from such an animal. Captain Jonathan Archer, in conversation with Doctor Phlox, accused the Denobulans of being insensitive, due to them eating the lemurs, which closely resembled Terran dogs. Archer thereafter gave Phlox an apology for having accused the doctor's entire species, though Phlox clarified that he couldn't speak on behalf of the other Denobulans, despite personally accepting the apology on his own behalf. (ENT: "A Night in Sickbay")
The Denobulan lullaby was a form of song. In 2154, Phlox offered to sing one of these lullabies to Porthos, although the doctor remembered that his singing had often made his Denobulan children cry. (ENT: "Storm Front")
Denobulan medical ethics considered a patient's will to be absolutely binding, including his refusal to be cured or live. This was much unlike the Hippocratic Oath followed by Humans, which compelled a physician to save a patient. (ENT: "The Breach", "Bounty") By the 22nd century, the Denobulans had experimented with nanotechnology. (ENT: "Regeneration")
Though typically embracing a full range of emotions, Denobulans seemed to highly value optimism and cheerfulness. However, they could also be deceitful, and their temper was sometimes furious. (ENT: "Broken Bow", "Stigma", et al.)
The Denobulans who resided on their homeworld included neurosurgeons and quantum theorists of varying qualities. (ENT: "Twilight") On Denobula, dermal art was very common until sometime before 2153. (ENT: "Stratagem") The native Denobulans did not keep pets, nor did they commonly play monkey-in-the-middle. (ENT: "A Night in Sickbay", "Stigma") They did, however, take delight in bequeathing their belongings to far-flung relatives. (ENT: "Zero Hour")
Anatomically, Denobulans were considerably more complex than Humans. Denobulans had prominent facial ridges running down either side of the forehead to the cheeks, an enlarged brow ridge under a high receding hairline, a vertical crevice in the center of the forehead, and a ridged chin. (ENT: "Broken Bow", et al.) They had ridges on their back along the spine. (ENT: "Doctor's Orders") Their toenails were dark brown and yellow striped. (ENT: "A Night in Sickbay", "Doctor's Orders") Denobulans had to trim their toenails at least once a week, due to the nails' extremely rapid growth rate. Denobulans also had very long tongues, and they used tongue scrapers. (ENT: "A Night in Sickbay")
Denobulan males had a line of hair down the middle of their chest, up to their neck. Similar brown streaks could be found running down the spine ridges on the back, as well as on the feet and on the back of both arms. (ENT: "Bounty", "A Night in Sickbay") The skin was much like that of Humans and Xindi-Primates. (ENT: "The Xindi")
Denobulan females had very potent pheromones that the males could sense, and they released them when they were romantically interested in someone, and presumably during their mating season. Denobulan males were known to become violent during the mating season. (ENT: "Dear Doctor") Anatomically, Denobulan males were also sexually compatible with both Vulcan and Human females. (ENT: "Bounty", "E²")
Denobulans had a unique ability to enlarge their faces. This was an instinct for when they felt threatened. (ENT: "Home") They could also display an unusually wide smile for humanoids. (ENT: "Broken Bow", "A Night in Sickbay", "Stigma", "These Are the Voyages...")
Denobulans normally required very little sleep, but they did hibernate for a sleep cycle of five to six days each year, although two days were sufficient as a bare minimum. If a Denobulan was nearing a sleep cycle, they might experience bouts of dizziness as a consequence. Deep hibernation resulted in the sleeping Denobulan becoming unresponsive to noises, regardless of how loud they were, but they could be awakened via a particular drug delivered intravenously. If a Denobulan was awakened prematurely, the results could be somewhat unpredictable; hibernating Denobulans, if woken, appeared extremely disoriented and confused, with oddly pitched voices, and had difficulty maintaining normal motor skills and cognitive functions. (ENT: "Dear Doctor", "Two Days and Two Nights", "Similitude", "Bound")
A Denobulan's sleep cycle could be affected by a type of pheromone emitted by Orion slave girls, making the Denobulan's body react as if their annual sleep cycle was imminent. This could affect a Denobulan to such an extent that the person required stimulants to keep awake. The longer the Denobulan was exposed to the pheromones, the more pronounced the reactions became. (ENT: "Bound")
Denobulans had highly efficient natural climbing abilities similar to those of Earth lizards, being capable of scaling vertical rock faces at a rapid speed with no equipment whatsoever. In this manner, a Denobulan could appear to scuttle up a rock face without needing to find handholds. (ENT: "The Breach")
Denobulans appeared to possess particularly powerful immune systems; when Phlox was nearly assimilated by the Borg, his immune system was able to fight off the nanoprobes long enough for him to find a means of destroying them, although he admitted that his immune system would not be able to hold them off indefinitely. (ENT: "Regeneration")
Denobulan life spans were extremely long, though a Denobulan elder did not necessarily look particularly old. (ENT: "A Night in Sickbay") Phlox, in the 22nd century, once stated that his grandmother lived through the last of numerous wars Denobula fought with the Antarans, a conflict which ended while Earth was in the 19th century. This indicates that at least three generations of Denobulans had existed during the three-hundred-year span between the events. (ENT: "The Breach")
Denobulan neurophysiology was about as resilient as that of Humans but less so than that of Vulcans. Thus, disruptions throughout a Denobulan's neocortex would probably be lethal, though a Vulcan could withstand such disruptions, merely being rendered unconscious. As a result, a Denobulan, like a Human, could probably be killed by Rajiin's telepathically caused disruptions throughout their neocortex, which was not necessarily fatal for a Vulcan. (ENT: "Rajiin")
Denobulan physiology was incompatible with wisps. No matter how much one such entity tried to invade a Denobulan's mind, it could not do so. Attempting such a procedure left no lasting effect on the Denobulan's physiology. (ENT: "The Crossing") On the other hand, Denobulans could be inhabited by Organian and were susceptible to having their memories altered, so that they retained no memory of the incident afterwards. Although one particular Organian once reckoned that Denobulan technology had enabled Doctor Phlox to detect that a pair of Organians were inhabiting two Humans, no such technology had been used in that case. (ENT: "Observer Effect")
In common with such species as Humans, Vulcans, and Ferengi, Denobulans could be drugged and rendered unconscious by anesthesia gas, such as when emitted from Ferengi gas canisters. (ENT: "Acquisition") Similarly, two Denobulan males who became overly aggressive with each other during the mating season could be separated using a dose of niaxilin. (ENT: "Dear Doctor") Another method of rendering Denobulans unconscious was a Vulcan nerve pinch. (ENT: "Singularity") A neural toxin delivered intravenously would terminate the Denobulan's synaptic functions within seconds. (ENT: "Regeneration")
Some indications suggest that Denobulans were particularly susceptible to certain types of radiation. When exposure to an exotic form of radiation caused almost the entire crew of the NX-class Enterprise to exhibit irrational and obsessive behavior, Phlox was the only senior officer whose actions nearly led to the deliberate death of another of his crewmates, as he was adamant about using surgical methods to discover why Ensign Travis Mayweather was suffering from a headache. (ENT: "Singularity") Furthermore, subjecting a Denobulan to a rather excessive dose of omicron radiation could be excruciatingly painful for the Denobulan. (ENT: "Regeneration")
Whereas trans-dimensional disturbances ordinarily caused disruptions in the Human neocortex, Denobulans were immune to their effects. The side effects of transdimensional disturbances that Denobulans were immune to included epidermal decay, which did affect not only Humans but also Vulcans. (ENT: "Doctor's Orders")
Denobulans could operate without food for considerably long durations. Eating not only enabled them to keep up their strength but also accelerated their cellular metabolism. (ENT: "Regeneration") A Denobulan could lose body weight by ingesting a Danaxian tapeworm. (ENT: "The Council")
The Denobulan doctor Phlox once claimed that the Denobulans were severely afflicted by thymic sclerosis and that it was "found in all strata of Denobulan society." This, however, was a deceit. (ENT: "Stigma")
The Denobulans believed they were the only intelligent species in the galaxy until the B'Saari made first contact with them. This incident thus came as quite a surprise to the Denobulans, many of whom took a while to accept the truth that they were not alone in the galaxy. Though it was a somewhat difficult process, the Denobulans were eventually forced to reevaluate their thinking. (ENT: "Future Tense")
Denobulans fought several wars against the Antaran species, the last of which occurred during the late 19th century. The Denobulans demonized the enemy, and their battle tactics killed twenty million Antarans. Both sides made faceless enemies of each other, and, although most had outgrown the past hatred, some Denobulans still held a grudge against Antarans as of the 2150s. (ENT: "The Breach")
A few hundred years before the mid-22nd century, the Denobulans had a form of entertainment that was similar to movies. When they discovered their real lives were more interesting, the Denobulans abandoned this type of media, having found it had lost its appeal. (ENT: "Dear Doctor")
The Denobulan use of genetic engineering, yielding results which were generally positive, began in or before the mid-20th century, and proceeded from then on. (ENT: "Borderland") The Denobulans who resided on their homeworld never came close to using genetic engineering to destroy one another. Possible reasons for this were multiple, ranging from the Denobulans being simply fortunate to the possibility that, by the time they started using genetic engineering, their instincts were synchronized with their intellect. (ENT: "Cold Station 12")
In 2115 or soon thereafter, a medical emergency occurred in orbit around Denobula when there was an explosion aboard a cargo ship which claimed more than 17 victims. Various medical teams helped to deal with the aftermath. (ENT: "Fight or Flight", "Damage") Also during the early 22nd century, the Denobulan Infantry was deployed in at least one conflict. (ENT: "Cease Fire")
Denobulans had contact with Humans as of the 2130s. By that time, they were cooperating within the Interspecies Medical Exchange (IME) and jointly operated Cold Station 12, although the Denobulans maintained a medical database of their own at least until 2154. (ENT: "Cold Station 12", "Observer Effect", "Demons")
In 2151, Denobulan doctor and IME member Phlox, who had until then been stationed in San Francisco on Earth, was assigned to be the chief medical officer of Humanity's first warp five starship, Enterprise NX-01. (ENT: "Broken Bow") In 2153 there were no Denobulans in the city of Atlanta. (ENT: "The Xindi") As of November 2154, there was a Denobulan ambassador assigned to Earth. (ENT: "Affliction")
In an alternate timeline wherein Jonathan Archer was infected by interspatial parasites, some of the greatest neurosurgeons and quantum theorists on Denobula were consulted by Phlox in an attempt to find a treatment. They believed it was impossible to eliminate the parasites without also killing Archer, and correctly assured Phlox that the technology to eradicate the infestation did not exist. The parasites were eventually destroyed due to a suicidal sacrifice by Archer, bringing an end to the alternate timeline. (ENT: "Twilight")
In the mirror universe, Denobulans were a slave race of the Terran Empire. A manifestation of the Denobulans' political alignment with the Empire was that the Denobulan Phlox served aboard the ISS Enterprise (NX-01) as the ship's doctor. The Denobulans were not part of a rebellion which opposed the Empire, as it was not in their nature to rebel. In 2155, the fact that the Denobulans of the prime universe were considered equal to the Humans and Vulcans was learned by residents of the mirror universe, including T'Pol and Phlox. Although they helped the rebels sabotage the commandeered USS Defiant during Jonathan Archer's attempt to overthrow the Emperor, Phlox did so in the hopes that the Emperor would reward him with concubines. (ENT: "In a Mirror, Darkly, Part II")
- Denobulan-Antaran wars
- Denobulan Infantry
- Denobulan language
- Denobulan lemur
- Denobulan lullaby
- Denobulan medical database
- Denobulan medical ship
- Denobulan sausage
- Denobulan Science Academy
- Denobulan shuttle
Originally the Denobulans were to have been called "Noorians", which they were named in a series bible from July or August 1999. The same document indicated that some of them would have played a role in Captain Archer's backstory, having rescued eleven of his crewmates in escape pods fleeing an attack by Suliban several years beforehand, during the "warp two era."
Later in the early development of Star Trek: Enterprise, the Denobulan species wasn't named. Both a subsequent draft of the ENT series bible and the script of Enterprise's pilot episode, "Broken Bow", omitted any reference to the species' name, merely describing Phlox as "an exotic-looking alien."  Furthermore, Enterprise's creators did not at first provide a detailed description of the species. According to Phlox actor John Billingsley, the reason was that the production staffers were "swamped." (Star Trek Monthly issue 84, p. 42)
Upon auditioning for the role of Phlox, John Billingsley reckoned that the alien character's species was "some kind of birdlike creature." This impression provided a basis for the actor's initial performances as Phlox, which involved him occasionally squawking.
Although a subsequent discussion which John Billingsley had with executive producers and show creators Rick Berman and Brannon Braga concerned Phlox's philosophical attitude in general, it did not relate to his species. "We didn't really talk at all about the background of my species or why we haven't encountered this species before," offered Billingsley. (Star Trek Monthly issue 86, p. 27)
Following this conversation with the series creators, Billingsley formulated his personal interpretation of Phlox's kind. Shortly afterwards, he explained, "My own sense is that it's a race of people who are hyperintellectual philosophers who have, in effect, chosen a monastic existence, and have decided to kind of hide away from the rest of the universe because they've got bigger fish to fry inside themselves!" (Star Trek: The Magazine Volume 2, Issue 7, p. 28) The actor further commented, "I see Phlox as from a planet where everyone is a teacher and philosopher. Everybody is navel-gazing. But one of the problems with navel-gazing is that it can make one insular and withdrawn from outside events." (Star Trek: Communicator issue 135, p. 33) Billingsley also supposed, "I don't think my species tends to make what I would consider the artificial distinctions that we tend to make between disciplines [such as anthropology, philosophy, and medical sciences]." (Star Trek Monthly issue 84, p. 42)
John Billingsley thought the highly detached aspect of his imagined version of the species might canonically explain why the Denobulans had never been depicted on Star Trek before the advent of Enterprise. He fully expected that the species would be explored by the series creators in such a way as to contradict his own concept of the group, an eventuality he was prepared for. With a laugh, however, he also said of his idea, "Maybe if I say this enough times, they'll subscribe to it themselves." (Star Trek Monthly issue 84, pp. 42 & 43) Moreover, Billingsley posited that his notion of the species might work well with the way the producers conceived of it, remarking, "[Brannon Braga]'s feeling is that the Denobulans are very advanced and very happy and very positive. One can speculate from that that they simply don't really have a tremendous need to be involved in the affairs of the universe. I mean, maybe it's so Eden-like [on Denobula] that it's like, 'Oh, what do I want to go out there for? I've got everything that I want right here.'" (Star Trek Monthly issue 95, p. 43)
The name Denobulans was first canonically established in ENT: "Terra Nova", the fifth episode of Enterprise, but a Denobulan appears in the first four episodes of the series. The only installment of those four to make reference to the group is the second one, "Fight or Flight", in which Phlox talks about "people" on his homeworld (the reference in "Terra Nova" is much more direct, with him literally stating, "I am a Denobulan," upon introducing himself to Novans).
During the course of the series, the writing staff of Star Trek: Enterprise exercised extreme caution in regards to establishing facts about the Denobulans. John Billingsley approved of this course of action, believing that the mysterious quality of the species helped make Phlox intriguing. (Star Trek Monthly issue 100, p. 7) "I was interested in what little we did learn about the Denobulan culture [including their polyamorous nature]," Billingsley acknowledged. (Star Trek Magazine issue 182, p. 32) He conjectured, too, that the producers similarly believed there was merit in keeping information about the species to a minimum. "I suspect that they feel tidbits every now and again might keep people's curiosity up," he hypothesized, "as opposed to doing an entire episode about Denobulan society that perhaps by revealing too much information may actually squelch people's interest." In ENT Season 1, Billingsley nonetheless pitched a couple of story ideas to the writing staff about the Denobulans on their homeworld. (Star Trek: Communicator issue 152, p. 24) He actually spent much of that initial season imagining what the planet's anthropology would be like. (Star Trek Magazine issue 182, p. 32)
Billingsley's suggestions of Denobulan-related plot concepts weren't accepted. (Star Trek: Communicator issue 152, p. 24) At the time, he noted, "Some of my own thinking has been contradicted by the scripts that have emerged, so I'm much less prone to spout off about it now in interviews!"  The actor elaborated after the fact, "The writers were making it up as they went along, as I was [....] So I learned that it was really not valuable for me to spend a lot of time speculating about unexplored avenues since, if they did explore avenues, they did so in very different ways than I'd imagined." (Star Trek Magazine issue 182, p. 32)
In the first draft of season one installment "Dear Doctor", it was said that many Denobulan children had been fathered by Phlox. "I still like to think of that as true, but it's not referenced in the script," stated John Billingsley, shortly after the making of the episode. "Beyond that, no, you don't really get a sense of the [Denobulan] culture [...] yet." 
In the writers' first draft script of "Dear Doctor", Phlox stated, "All Denobulans are quite similar." However, this wasn't widely known to Humans. (Cutler was unaware of it, and Phlox supposed Doctor Lucas, now that he was actually serving on Denobula, was finding out for himself the remarkable degree of similarity in the species). The same writers' first draft script also established that individual Denobulans were named for whichever profession they were born into.
In dialogue which was eventually omitted from the final draft script of "Dear Doctor", Phlox and Archer imagined the Denobulans facing extinction, and T'Pol later mentioned that Vulcan medical techniques were no more advanced than those employed by the Denobulan doctor.
While appearing on Comedy Central's The Daily Show on Monday 11 February 2002, Scott Bakula described Denobulans as "some kind of bird/reptile." Also, host Jon Stewart jokingly suggested that the typically polygamous nature of Denobulans made them similar to Mormons.
By the end of Enterprise's first season, John Billingsley had to revise some of his notions about the Denobulans. In an interview from February 2002, the actor reflected, "It's interesting when you have to do a back-story on a whole civilization. It's intriguing that the thoughts I had initially on the nature of their civilisation I've already had to modify a bit." 
Even though the name "Denobulan" was used fairly often in the series, the script of "Stigma" included the word in its pronunciation guide.  Before the first Denobulan woman was portrayed in that episode (Feezal, who was also the first Denobulan other than Phlox to ever appear on-screen), John Billingsley repeatedly joked that he would like his wife in reality, Bonita Friedericy, to play all Denobulan women that appeared on the series. Billingsley thought that would be "fun", would allow his wife to feature in many episodes, and would supply the couple with more residual checks. Billingsley also wanted any Denobulan males that showed up on the series to be played by himself. "That way, everybody on Denobula was either John Billingsley or Bonita Friedericy," he later related. 
John Billingsley's thoughts on the Denobulans included speculations about their sexuality. In an interview with Dreamwatch magazine, the actor referred to the Denobulans as "known bisexuals," although that differs from how they were represented in canon. Also, Billingsley once humorously speculated to the series' writing staff that, due to Phlox's having three wives, he would likely have "three members." Even though this idea concerning Denobulan sexual organs was not adopted by the writers, the conversation in which Billingsley suggested it led to more of the Denobulan physique being shown on-screen, in "Doctor's Orders", than had ever been depicted before. (Star Trek Magazine issue 115, p. 36)
A Denobulan-related line of dialogue which was not in the final draft script of "The Breach" but is in the final version of that installment involved Phlox shouting at Antaran patient Hudak, "No Denobulan would want to be in the same room with you!"
The backstory involving the Denobulans' war with the Antarans, as established in "The Breach", did not meet the approval of John Billingsley. He critiqued, "I think coming up with an episode where Denobulans were once war criminals, there was still this credible anger that had not been resolved, it seemed to me at least – and maybe some of the fans too – a little too jarring, a little too difficult to jive with what we knew about Phlox." Billingsley added that, although there were some elements of the script for "The Breach" that he found fault with, the Denobulans' warfare had somewhat been alluded to in previous installments, such as a reference to the Denobulan Infantry in "Cease Fire".  In fact, even the existence of a Denobulan military came as a surprise to Billingsley. (Star Trek: Communicator issue 152, p. 22)
By the end of the second season, there was some fan speculation that the Denobulans were later to be revealed as the Cardassians going under a different name, despite the lack of on-screen evidence to support this theory. (Beyond the Final Frontier, p. 380) The question of whether the two species were related was, according to John Billingsley, never discussed. 
The only performer to make appearances as multiple Denobulans was regular background actress Nikki Flux, who played members of the species (in an uncredited capacity) in "Cold Station 12" as well as the two-parter "Demons" and "Terra Prime". Two different Denobulan characters were portrayed by her in these episodes, but neither of them was named.
In contrast to his satisfaction with the way in which the writing staff released scraps of information about the Denobulans every so often, John Billingsley conceded that, had he been given the chance to contribute story material for the series, it would have revealed more about the Denobulans. In a retrospective interview, he said that he would have liked to learn more about the Denobulans' culture and belief systems.  Left to ponder the mystery of what finally happened to the Denobulans, Billingsley mused, "There are no Denobulans in the future, apparently. I think we were an inbred species and I guess we eventually went the way of most inbred societies." 
If Star Trek: Enterprise had gone on to a fifth season (rather than being canceled after its fourth one), the Denobulans would likely have been shown in greater depth than they ultimately were, because shortly before the cancellation was announced, Manny Coto voiced an interest in visiting Denobula in the fifth season.  Another concept which was ultimately never established also concerned Denobulan society, as Executive Story Editor André Bormanis suggested that other Denobulans weren't permitted to receive medicine from Phlox or be operated on by him, as he was actually a veterinarian on Denobula. ("Countdown" audio commentary, ENT Season 3 Blu-ray special features) Denobulans were additionally to have appeared in the film Star Trek: The Beginning, but would not have played a critical role in the plot of that movie, which was ultimately abandoned. 
When starting to imagine what a Denobulan's face might look like, Makeup Supervisor Michael Westmore was guided by advice that each of the actors playing the aliens was to have only a subtle makeup job. "The producers wanted him [or her] to look a little more Human than some of the characters from the past, like Odo or Neelix," Westmore recollected. Working out the details of this facial design took considerable effort, however. "We really didn't know what we wanted [...] so I hired five other artists, all sketching away for two weeks, and I ended up filling a notebook with more than 80 sketches," stated Westmore. "I'd literally come home and [Westmore's wife] Marion would say, 'Go in the other room and draw!' and the other guys would be faxing me their sketches over the weekend and I'd call them back and say, 'That's the direction we want to go; keep going that way.' It seems that everyone wanted to get more flamboyant and larger than life, and I knew that wasn't what Rick and Brannon wanted, but would feed me into ideas that I could show them and know what they really wanted." (Star Trek Monthly issue 98, p. 43)
Eventually, makeup and other appliances were used to accentuate the actor's forehead, chin, ears and own hair with extensions and alien shaping. (Star Trek: Communicator issue 135, p. 34) "I decided to enhance the edges of his [or her] skin with a little Dax-like pattern," Michael Westmore explained. The actor also wore contact lenses that increased the brightness of his or her eyes, though their natural basic skin tone was retained for their Denobulan appearance. (Star Trek: Communicator issue 135, p. 67) Whereas the actor's own hair was also included in their Denobulan look, the performer wore three separate prosthetic pieces, along with the contact lenses. These parts consisted of an artificial forehead, chin and ears, all of which were painted over in a variety of shades. (Star Trek Monthly issue 86, p. 28) According to Westmore, the fact that the makeup worn on the actor's face was mostly restrained to above their eyes was due to the producers' decision to have the makeup be relatively minimal. Similarly, Westmore reflected that he added the small chin piece "for balance" and that the contact lenses were intended "to give us something different." (Star Trek Monthly issue 98, p. 43)
The process of applying the makeup required for the Denobulans' alien demeanor originally took three hours but had been shortened to two hours by the time the species received its name. (Star Trek: Communicator issue 135, p. 34) "The prosthetics they can do in 15 or so minutes," clarified John Billingsley, "but it's the actual painting and modelling that takes a while." (Star Trek Monthly issue 86, p. 28)
John Billingsley was impressed by his first sight of the Denobulan makeup, as sported by himself. "I thought it looked terrific. I thought I looked kinda sexy in a way!" the actor reminisced with a chuckle. "I'm not sure anyone else will echo those feelings." (Star Trek Monthly issue 86, p. 28)
Even from the outset, the Denobulan makeup was extremely comfortable to wear. (Star Trek Monthly issue 84, p. 23) John Billingsley noted, "It hasn't been a problem at all." He also considered himself "lucky" that, unlike certain other Star Trek performers, he did not have to wear a huge amount of rubber, nor dentures which might have brought him pain. (Star Trek Monthly issue 86, p. 28)
To demonstrate Denobulan feet in "A Night in Sickbay", new foot prosthetics were donned by John Billingsley. For the female variant of the Denobulan facial makeup, Michael Westmore slightly streamlined the male version in order to make it a little bit more attractive-looking. ("Stigma" text commentary, ENT Season 1 DVD)
In accordance with the script for "Singularity", the novel Surak's Soul establishes that Denobulans are more susceptible to radiation sickness than Humans. The same book also indicates that Denobulans have their own standard form of radiation treatment, despite also having a very similar skeletal structure to members of the Human species.
The novel Daedalus's Children establishes that a male Denobulan named "Parnikee" was an esteemed and highly accomplished scientist. He invented the matter/antimatter engine on the planet, led the first Denobulan exploratory vessel, and predicted the existence of parallel universes. Parnikee also provided at least the namesake for Parnikee's Theorem – a Denobulan theory that set forth the rate of the universe's expansion, an equivalent of the Hubble Constant – though it is unclear whether he was personally involved in devising that theory.
The novel Rosetta includes Phlox relating, to several of his crewmates aboard Enterprise, an unfortunate story that concerned a delayed shipment of antibiotics to a Denobulan colony, with the Thelasian Trading Confederacy at fault.
Star Trek: Federation - The First 150 Years (pp. 73, 75, 81, 85 & 103) mentions the Denobulans as one of the first species to visit Earth after Vulcans had. The publication also states that the Denobulans were of strategic importance to the Romulan Star Empire during planning of the Earth-Romulan War in 2156, as the Denobulan system provided a potential staging area from which the Romulans could launch an attack against Earth. Since the Denobulans were not at war with Romulans nor officially allied with Earth, Praetor Gileus and his military advisers expected that the species would be unprepared for an ambush and easily defeated.
On October 1st 2158, all Denobulans aboard an orbiting spaceport which the species had been maintaining were killed by officers who boarded the facility from a fleet of ten newly arrived Romulan battle cruisers. The Denobulans on their homeworld were warned not to interfere by Romulan naval chief of staff Admiral Mindar, who led the invasion and was aware that the Denobulans were reputed to be fierce fighters when necessary. Under his orders, over three million Denobulans were subsequently killed in a devastating strike against their planet's sole continent; Mindar hoped to not only demonstrate the superiority of the Romulans' military power but also to keep them busy, further minimizing the chance of their retaliating during the onslaught against Earth.
Though this proved effective, the Denobulans, owing to the attack on their homeworld, were persuaded by Human politician Nathan Samuels to join the war effort. Thus, several Denobulan warships were deployed as reinforcements when Starfleet retaliated against the Romulans. Joining the Warp-5 Starfleet ship Lexington, the Denobulan vessels entered Romulan space and, as the Battle of Cheron raged, headed for Romulus. The combined approach towards the Romulan homeworld panicked Gileus into surrendering, bringing an end to the war. After the Federation was founded, Denobula considered joining for many years. However, an act of hostility, wherein a Klingon warship attacked and destroyed a Denobulan freighter that the Klingons claimed had been violating their territory, led the Denobulans, still recovering from the Romulan War, to withdraw from galactic affairs.
Several Star Trek novels set in the 24th century have Denobulans in them. Some references include the Star Trek: The Lost Era novel The Sundered, which has a Denobulan engineer on the USS Excelsior. A dead Denobulan is featured in the second novel of the Star Trek: Vanguard series, Summon the Thunder. One of the USS Enterprise-E's doctors, Tropp, is a Denobulan in the Star Trek: A Time to... series.
In the game Star Trek: Elite Force II, several Denobulans are among the crew of the Enterprise-E.
The tutorial level for Federation characters in Star Trek Online features player characters going on a training cruise under Denobulan Captain Masc Taggart. Also, the Player may set a custom holographic officer to appear as a Denobulan (among other races). Captain Kuumaarke also mentions that the Denobulans were the second species to assist the Lukari when they reached for the stars for the second time after the Kentari/Lukari civil war, first one having been the Ferengi "... for a price, of course!". Finally, some other NPCs (unique and randomly generated) are Denobulans but they are in very limited number and none have a significant impact on the Player's progress past the tutorial.