(covers information from several alternate timelines)
The Suliban were a largely nomadic warp-capable humanoid species, considered by the Vulcans to be "a somewhat primitive species". (ENT: "Broken Bow", et al.) They were notable during the mid-22nd century for their involvement as foot soldiers in the Temporal Cold War, which brought them into conflict with several other civilizations, including United Earth.
Suliban of the Cabal received extensive physical enhancements via genetic engineering delivered from a mysterious humanoid from the far future. These enhancements varied among individuals and could include greatly increased flexibility in all parts of the body, the ability to cling to walls and ceilings, the ability to alter the color and texture of their skin for camouflage or to mimic other humanoids, compound retinas granting enhanced vision, increased numbers of bronchial lobes with modified alveoli clusters for processing different atmospheres, and the ability to tolerate vacuum. An ex-Cabal agent, Sarin, could measure trust by physical contact – a seemingly passionate kiss, in the case of Jonathan Archer. (ENT: "Broken Bow", "Cold Front")
The Suliban homeworld, located in Sector 3641, became uninhabitable in the 1850s. Most Suliban adopted a nomadic lifestyle, while some settled in the territories of other species, such as in the Tandar sector, and assimilated into the local populace. (ENT: "Broken Bow", "Detained")
At some point, a group of Suliban came into contact with a mysterious figure from the 28th century, who represented a faction in the Temporal Cold War. This individual offered physical "evolution" and advanced technology to the Suliban in exchange for their service. These Suliban formed the Cabal and began to carry out clandestine attacks designed to destabilize various powers in the region, such as the Klingon Empire and the Tandarans. (ENT: "Broken Bow", "Detained") The Cabal opposed various other factions in the Temporal Cold War, including the Tholians, the Sphere-Builders, and the Na'kuhl, whose leader Vosk once attempted to disrupt the evolution of the Suliban into a sentient species. (ENT: "Future Tense", "The Expanse", "Storm Front, Part II")
In April 2151, two Suliban agents pursued the Klingon courier Klaang to Earth in an attempt to prevent him from carrying intelligence about Cabal activities to the Klingon High Council. During the ensuing Broken Bow Incident, they were killed in an explosion caused by Klaang. The Suliban subsequently attacked the NX-class starship Enterprise but were ultimately unable to prevent the craft from delivering Klaang to Qo'noS. (ENT: "Broken Bow") The Suliban Cabal encountered Enterprise on several subsequent occasions; for example, in 2152, they attempted to frame the ship's crew for destroying a colony on Paraagan II and fought Enterprise to acquire a 31st century Earth vessel. (ENT: "Future Tense")
The activities of the Cabal soured perceptions toward the Suliban people as a whole. Some began to see all Suliban as potentially dangerous monsters, due to the modifications of Cabal soldiers. These sentiments stirred resentment in uninvolved Suliban toward both the Cabal and their former neighbors of other species. After Cabal attacks began in 2144, the Tandarans began to inter their resident Suliban in detainment camps, ostensibly for their "protection." (ENT: "Detained")
However, the Suliban Cabal was able to obtain various advanced technologies from their benefactor from the 28th century, including cloaking devices and genetic engineering techniques. Genetic enhancements could be given to or removed from individual Suliban at will for reward or punishment. The Cabal operated from massive space stations called helixes and had available large numbers of small, stealthy cell ships armed with high-yield particle weapons. Some Suliban ships were powered by tricyclic plasma drives. Cabal soldiers wore a bio-mimetic garment that could change in appearance, complementing the soldier's own shapeshifting abilities. (ENT: "Broken Bow", "Cold Front", "Shockwave")
- Suliban cell ship
- Suliban freighter
- Suliban helix
- Suliban pistol
- Suliban rifle
- Suliban shuttle
- Suliban stealth cruiser
- Suliban transport
Depicting the species
The name "Suliban" was coined by Rick Berman, after the Taliban, months before the September 11, 2001 attacks. According to Berman, the "Taliban was just a mysterious, exotic name to me. Several years ago, I went to Afghanistan. I used to make documentary films and traveled around the world, and the Taliban regime was just getting a stronghold there. To me, there was something incredibly dramatic about the name Taliban. It was like something out of a Sinbad story." (TV Guide, May 5-11, 2002 ed.; )
According to internal documents, the Suliban were originally planned to appear in Star Trek: Voyager's sixth season, in preparation for their appearance in ENT. A backstory was even planned involving the Borg decimating their homeworld in the 23rd century, forcing them to relocate to the Delta Quadrant, helped by mysterious time travelers. 
When the Suliban were introduced in the script of "Broken Bow", they were referred to as "a genetically engineered species with an unusual dappled texture to their skin."  Similarly, in the final draft script of "Detained", they were introduced with the description, "Their skin has a familiar texture, dappled and hairless."
Due to having to determine the skin tone of the Suliban, the species turned out to be the most challenging for veteran Star Trek Makeup Supervisor Michael Westmore to create in ENT Season 1. "I was given a photograph of a computer-generated image from a magazine of what [producers] Rick Berman and Brannon Braga were interested in, and I had to try to develop this skin tone," Westmore remembered. "It took about a week and a half of experimenting to figure out how to do it. If you sat down and tried to sculpt something like that, it would have taken a year to try to do all that little work." (Star Trek: Communicator issue 139, p. 45)
Eventually, a solution for creating the dappled Suliban skin was discovered. "We figured out a way of making these thin, pebbly skins and laying them over the basic clay structure," explained Michael Westmore. "Then we went and made molds by taking these skins and laying the molds in for lips, eyelids, ears, chins, backs of hands, fingers – every part of the body. So the make-up was done in sections, and each [body part] had a different mold that we'd pour rubber into. Even in pouring the rubber into the molds, there was a lot involved." (Star Trek: Communicator issue 139, p. 45)
Concerning the Suliban makeup, Silik actor John Fleck stated, "Your eyelids and the bottom of your eyes and your chest is all glued down." The makeup also involved contact lenses. (Star Trek: Communicator issue 139, p. 41)
The shapeshifting abilities of the Suliban were made possible by CGI. ("Broken Bow" text commentary, ENT Season 1 DVD/Blu-ray) At least for "Broken Bow" (if not also other episodes), Visual Effects Producer Dan Curry created these effects. ("Broken Bow" audio commentary, ENT Season 1 DVD/Blu-ray)
There was definitely a standard way of naming Suliban, so much so that, in the final draft script of "Detained", Tandaran Major Klev remarked that the name Malcolm "doesn't sound like a Suliban name."
To depict the Suliban in "Detained", nineteen makeup layouts were required, an unusually heavy workload for the make-up department to create for the Suliban. Michael Westmore therefore needed to bring in extra help. Near the end of that first season, the make-up for another sixteen Suliban was called for. Owing to the sheer quantities of Suliban as well as other aliens, Westmore had to hire an additional twenty-five crew members to assist his regular make-up staffers, of whom there were four. (Star Trek: Communicator issue 139, p. 45) According to Star Trek: Communicator issue 139 (p. 45), the sixteen Suliban were to appear in the season's penultimate installment, "Two Days and Two Nights". However, the Suliban do not appear in that outing and are merely referenced therein, their next appearance being first season finale "Shockwave".
At the conclusion of ENT's first season, Brannon Braga believed "a lot about the Suliban" had been revealed in "Detained" and he remarked, " I think the Suliban turned out to be a very interesting race." (Star Trek: Communicator issue 139, p. 29)
The Suliban were ultimately featured a lot less than they originally were intended to be. Stated production illustrator John Eaves, "The Suliban were a strange race and they were to be so prominent in the new series, but by season 2 they had pretty much faded away."  In fact, the Suliban seemed to have settled down by the 23rd and 24th centuries, as they are not seen in any series other than Enterprise, and are mentioned only once outside of Enterprise (in LD: "Cupid's Errant Arrow"). Early in the series' development, the creators hinted that the audience would learn the fate of the Suliban species (and why they never appeared outside the prequel series), but that too must have been changed when the Temporal Cold War arc was prematurely ended in Enterprise's fourth season.
A letter from Danik's wife to he himself was, as evidenced by the final draft script of ENT: "Detained", meant to be written in the Suliban language. However, the contents of the letter cannot be clearly seen in the episode's final edit.
A sheet with Suliban script remained in Hoshi Sato's quarters aboard Enterprise. The sheet was part of a bulletin board which was sold off on the It's A Wrap! sale and auction on eBay.  Also sold at the same sale and auction were a Suliban interrogation device, seen in "Broken Bow" and "Shockwave, Part II", , a Suliban wall panel , and a special effects make-up head wrap.