(covers information from several alternate timelines)
In the early 2150s, the Xindi Council committed an infamous attack on Earth and made repeated attempts to terminate Humans, which changed the course of history and initiated a series of events that helped establish United Earth as a major interstellar power. In at least one future timeline, from where Daniels originated, the Xindi state had, by the 26th century, become a member of the United Federation of Planets.
"Five? Hm... I suppose there are, now."
Six different intelligent species developed on Xindus; one of them, the Xindi-Avians, was believed extinct by the 2150s, as the result of a brutal civil war between the six species that destroyed the planet. (ENT: "The Shipment") The surviving species were united under the governance of the Xindi Council, which contained two representatives from each species. (ENT: "The Xindi", et al.) The five remaining species were:
Each of these five remaining species had their own distinct opinion about which was the dominant species, all separately favoring their own. (ENT: "The Xindi") There was, therefore, an enormous amount of conflict and distrust between the species. (ENT: "Exile") However, the Arboreals and Primates tended to quarrel the least, with most conflict centering on the aggressive Reptilians and Insectoids, or the indecisive Aquatics.
The different Xindi species were extremely similar in their functionally important DNA, sharing over 99.5% despite the apparent physical differences. (ENT: "The Xindi") All the Xindi species shared distinctive ridges on their cheekbones and foreheads. (ENT: "The Xindi", et al.)
- Main article: Xindi history
The Xindi had a long and turbulent history, characterized by interspecies conflict up until the destruction of their homeworld in the 2030s as the result of an Insectoid and Reptilian plot. (ENT: "The Shipment") In the 2150s, they attempted to destroy Earth with a massive weapon. (ENT: "The Xindi", et al.)
The Xindi practically worshiped the Guardians, considering them saviors. Children were taught to revere them and give thanks to them at the end of each day. It was a terrible offense to question a Guardian. (ENT: "The Council")
The Primates, Arboreals, and Reptilians spoke a common language that was recognized by Starfleet universal translators. The Insectoids and Aquatics understood this language, but appeared to be physically incapable of speaking it. Consequently, the Primates, Arboreals, and Reptilians were forced to learn the Insectoid and Aquatic languages.
The Xindi were originally not as varied as they became. "At first, there was only going to be one particular race of Xindi," reported Star Trek: Enterprise concept illustrator John Eaves. (Star Trek: The Official Starships Collection, issue 24, p. 11) Executive Producer Brannon Braga spent a very long time mulling over the concept which was later to develop into the Xindi. His initial idea was speculating what it might be like if, on Earth, Humans had not been the only lifeforms to develop intelligence but species such as dolphins, insects and other primates had too. (Uncharted Territory, Part 3: Course Correction, ENT Season 2 Blu-ray special features) Braga admitted, "I always wonder, 'What would Earth have been like if dinosaurs had evolved to become intelligent? And not only that but insects, birds.... What if it happened, there was simultaneous evolution into intelligent organisms and they all lived together?'" (In a Time of War, Part Three: Final Conflict, ENT Season 3 Blu-ray special features) Braga added to these notions by imagining that such a collection of intelligent lifeforms, if alien, might have a grudge against Earth. "It just all kind of came together," he noted. (Uncharted Territory, Part 3: Course Correction, ENT Season 2 Blu-ray special features)
As a result of instructions on how to develop Star Trek: Enterprise – which came from Paramount Pictures, amid the second season – the opportunity to actualize the concept of an alien alliance comprising various related species finally arose. "I knew it was hard to pull off," admitted Brannon Braga. "But we'd just been given kind of carte blanche to maybe spend a little more money and do something big." (Uncharted Territory, Part 3: Course Correction, ENT Season 2 Blu-ray special features)
Co-Executive Producer Chris Black was involved in early discussions about the multi-species facet of the Xindi. Even though it had been decided that only one sentient dominant species would be depicted per planet, the notion of five sentient species who shared a planet was welcomed by the writing staff of Enterprise. ("Countdown" audio commentary, ENT Season 3 Blu-ray special features)
The concept of the Xindi was additionally inspired by the attacks on 9/11 and those responsible for them. Director David Livingston mused, "The Xindi were [...] destroying parts of Earth, so it was reflective of what was going on at the time." (In a Time of War, Part One: Call to Arms, ENT Season 3 Blu-ray special features)
Although a badly incinerated Xindi corpse appears in the second season finale "The Expanse" (which was scripted to have "animalistic features"), this effectively hid the fact that, by that point, no design for the physical appearance of the Xindi had been created. ("The Xindi" text commentary, ENT Season 3 DVD) Brannon Braga recollected, "In terms of who the Xindi were, that didn't come until after the break [between the second and third seasons]." ("The Xindi Saga Begins", ENT Season 3 DVD special features) Giving life to the Xindi, designing how they looked, took a total of about two months. (Star Trek: Communicator issue 149, p. 50) Commenting on the selection of the five specific species incorporated into the Xindi, Executive Producer Rick Berman stated, "They just were the ones that seemed right for us. It was just something Brannon and I developed; we knew that there was going to be the humanoids and the reptilians because we had touched on those, and then the other three came quite easy." (Star Trek: Communicator issue 147, p. 16) John Eaves offered, "By the time that the script came out we were going to do a multiple version [of the Xindi], kind of like people from different countries. Not necessarily different skin colors but completely different species of creatures, like insectoids, humanoids and so on. The insectoid and humanoid species were the first ones we started working on." (Star Trek: The Official Starships Collection, issue 24, p. 11) In the final draft script of ENT Season 3 premiere "The Xindi", the five species were described thus; "All of these Xindi are intelligent beings that evolved on the same planet, and though they are very different in appearance, they all share a subtle, unifying facial characteristic that hints at their common ancestry."
Because it obviously wasn't guaranteed that the Xindi would prove successful, Rick Berman expected the aliens might subsequently be eliminated from the series and he therefore came up with a contingency plan of devising numerous stand-alone episodes in which they were not involved. (In a Time of War, Part Two: Front Lines, ENT Season 3 Blu-ray special features)
From the very beginning, Rick Berman and Brannon Braga knew they wanted to depict the Xindi-Insectoids and -Aquatics using CGI. (Star Trek: The Official Starships Collection, issue 24, p. 14) This extensive use of visual effects technology, with both species typically being depicted entirely using computer-generated figures, tasked the VFX artists. "The challenge of the Xindi for the visual effects team," explained Visual Effects Producer Dan Curry, "was that we would be creating a pretty high volume of CG characters in a very short period of time." (In a Time of War, Part Three: Final Conflict, ENT Season 3 Blu-ray special features) Curry credited the animators and the CG technology involved with making this possible. (Star Trek: The Official Starships Collection, issue 65, p. 10) Curry recalled of the VFX artists, "We were very excited – we felt that now technology and what we've learned would enable us to do better quality work than we had done in the past with these [all-CGI characters]." (Star Trek: Communicator issue 149, p. 50) "A few years ago it would have been financially impossible to do," reckoned Rick Berman, midway through the third season. "What has happened now is that we have the technology and the people who can give it to us. The problem is that with our two CG species, the Insectoids and Aquatics, we will probably not see as much as we would like because of the expense." (Star Trek: Communicator issue 147, p. 16)
Much research and development was invested in the character design for the Aquatics and Insectoids, at the start of the third season. The CG artists were well-prepared for the challenge of visually creating the characters. Digital Effects Supervisor John Teska recollected, "I'd already heard that there was gonna be this race of Xindi that, of course, were going to be multiple different kinds of aliens. You know, we had heard that the Insectoids and the Aquatics were going to be CG." ("Visual Effects Magic", ENT Season 4 DVD special features) The task of designing these new beings went to Dan Curry. Although it's rare for a visual-effects producer instead of the art department to do any design work on Star Trek, Curry had proven he could deliver such work by having designed the Klingon bat'leth. He also had relevant experience of working with a full-CGI creature, in the form of Star Trek: Voyager's Species 8472. (Star Trek: The Official Starships Collection, issue 24, pp. 14-15) Thus, the process of designing the Aquatics and Insectoids began, in both cases, with sketches by Curry, prior to the CG artists developing these designs. The appearance of both species had to seem particularly alien, owing to Berman and Braga's concept of the Xindi. It was made the responsibility of visual effects artists at CGI vendors Eden FX to proceed with the designs. (Star Trek: The Official Starships Collection, issue 65, p. 10) Eden FX co-founder John Gross remembered, "We worked on [the Xindi insectoids and aquatics] together [with FX artists David Morton, Sean Scott, and John Teska], modelling them and rigging them and getting them working. It took a few weeks." (Star Trek Magazine issue 118, p. 30) Other Xindi species were occasionally represented with CGI, including Reptilians in some footage from "Countdown" ("Countdown" text commentary, ENT Season 3 DVD) and Arboreals in "The Shipment".
Costumes and sets
Virtually all the clothing worn by the Xindi was designed by Bob Blackman; this even included ambassadorial robes worn by the Insectoids, though Insectoid armor (the only exception) was designed by Dan Curry. (Star Trek: Communicator issue 149, pp. 50 & 51)
Under the aegis of Production Designer Herman Zimmerman, the art department had to design the look of the sets for each Xindi species. "That was a good challenge," said Zimmerman, "just because we had to make them different enough that you always knew where you were." (Star Trek: Communicator issue 151, p. 56)
The shipboard graphic layouts for the various Xindi species were designed to resemble each other (at least, in the case of the Xindi-Primates and Xindi-Reptilians). However, each species was given a different color scheme; the Reptilians had primarily blue control graphics, whereas the Primates had green ones, and the Insectoids' were colored red. ("The Xindi" text commentary, ENT Season 3 DVD) Herman Zimmerman offered, "We did do a lot of very specific Xindi graphics and, within the larger framework of the Xindi, each Xindi species had their variation of those graphics." (Star Trek: Communicator issue 151, p. 56)
Performing as Xindi
Of all the guest stars and recurring actors who featured on Star Trek: Enterprise, former longtime Star Trek casting director Ron Surma cited the group of performers who played recurring Xindi as a highlight, enthusing, "I liked the Xindi guys [...] Those guys were a lot of fun." Surma also pointed out that Randy Oglesby, Rick Worthy and Scott MacDonald had all made repeated guest appearances on Star Trek before portraying recurring Xindi.  The actors themselves were extremely grateful for the repeated opportunities to appear on the series. The fact that filming the Xindi Council scenes required full days, however, initially meant that the Xindi-playing performers did not meet any of the series' regular cast members (this remained the case until at least immediately after the production of "Rajiin"). 
With very little information available about the Xindi at the start of the third season (such as in the script for third season opener "The Xindi"), the actors cast to play the aliens "weren't sure how it would go," in Scott MacDonald's words.  "We were creating it as we went along which is both liberating and limiting," offered Xindi-Primate actor Tucker Smallwood. "That sort of thing takes agreement. Our directors change each week. You don't necessarily have that continuity, as you go from episode to episode." Therefore, some of the actors who played Xindi Council members (including Scott MacDonald, Rick Worthy, Randy Oglesby and Smallwood himself) devised much about the multiple species, at least for personal subtext. Continued Smallwood, "[We] would interact each time we worked together – not only try to find continuity but also create, so that we had someplace to go to and come from." Much of this inventing was during the group's long hours in make-up. "We teased about our rituals and having to make stuff up," Smallwood reminisced. One thing the performers decided was that, though the only Xindi species to be firmly established as including females were the Aquatics and Reptilians (with the Insectoids being an asexual race), other Xindi females do exist. (Star Trek: Communicator issue 151, pp. 51 & 52) Another element devised by the actors – specifically MacDonald and Oglesby, who played the leader of the Xindi-Reptilians and the leader of the Xindi-Primates respectively – was the hatred between the Reptilians and Primates, an idea the show's writers picked up on and began including in future scripts. 
The task of interacting with the imaginary Xindi-Insectoids and -Aquatics, later to be inserted into scenes with CGI, was fairly easy for the actors portraying Xindi-Primates, -Arboreals and -Reptilians. Related Tucker Smallwood, "Ultimately, it's not that different from naturalistic scenes, more often than not; on close shots, we're looking at a mark, rather than into the characters eyes. It's important to have an image in your mind's eye of the being to whom you're speaking." 
Despite Xindi having appeared in multiple previous episodes, the final draft scripts for Star Trek: Enterprise didn't identify any of the Xindi-playing performers until the advent of "Azati Prime". The final draft of that episode's teleplay described "a Xindi-Humanoid (Tucker Smallwood), an Arboreal (Rick Worthy) and a Reptilian commander (Scott MacDonald)." The same performers were also cited in the final draft script of follow-up installment "Damage", whereas the final draft script of "E²" cited Worthy and Smallwood as appearing in that episode. The final draft scripts of "The Council" and "Countdown" named both of those actors as well as MacDonald.
Tucker Smallwood, Scott MacDonald, Randy Oglesby and Rick Worthy became so used to seeing one another in their Xindi makeup that, upon meeting years after portraying their respective Xindi characters, they hardly recognized one another at first. 
Early reactions to the Xindi among the writing staff of Star Trek: Enterprise were highly positive. Chris Black reflected, "This idea that there were five sentient species who shared one planet [...] we all felt, at the time, sounded really cool [...] It satisfied, in a lot of ways, what people wanted to see, which was something new, a new alien race or races." ("Countdown" audio commentary, ENT Season 3 Blu-ray special features)
Rick Berman and Brannon Braga were highly proud of how the Xindi turned out. Braga remarked, "The whole Xindi species concept was really cool. That's a science fiction concept I'd never seen before. You had insects and aquatics with intelligence and culture. I thought that was a fascinating idea."  He further commented, "The five-specied Xindi is an interesting science-fiction concept that I think really worked out well. Each species was featured at some point along the way. They had internal strife. They're betrayed just like... They betray each other. It's like a Shakespeare play or something, backstabbing and all sorts of stuff going on." ("The Xindi Saga Begins", ENT Season 3 DVD special features) This duplicitous aspect of the Xindi's interrelationships was one of the group's many facets that Braga liked. "By the end the Xindi were a complicated, interesting and visually stimulating species," he opined. "I liked the way we gave each of the Xindi species its day in the sun, and even a sixth, extinct species got explored in a way." (Star Trek Magazine issue 117, p. 62) Shortly after Berman viewed the first completed shots of the Aquatics and Insectoids, he enthused of the footage, "It's far more than I expected. Considering the budget that is available to us, it's just spectacular stuff." (Star Trek Monthly issue 110, p. 15) He later raved about the various Xindi species, "I think they all look great." (Star Trek: Communicator issue 147, p. 16)
Consulting Producer David A. Goodman believed the three Xindi species which were portrayed using make-up were examples of extraordinary and "really remarkable" artistry by Michael Westmore. Director David Livingston agreed, "They were real." ("Impulse" audio commentary, ENT Season 3 Blu-ray special features) Goodman elaborated, "I think that it's interesting because, from a science fiction point of view, the idea of this one planet that had all these five different species who grew up into or evolved into intelligent species is a really cool idea but it's like the limits of science fiction [and CGI] on television [....] On the one hand, [the way the Xindi turned out was] kind of building on an audience's familiarity with these types of aliens. On the other hand, if you wandered into the show, for the first time, you'd be so confused [...] But it was sort of building on fans' comfortableness with these concepts." ("The Forgotten" audio commentary, ENT Season 3 Blu-ray special features) Goodman had another criticism about the Xindi. "I had a big bump on the fact that they, the Xindi, just didn't blow the ship [i.e. Enterprise] up. I felt like that was [obvious]," he laughed. (In a Time of War, Part One: Call to Arms, ENT Season 3 Blu-ray special features) Goodman specifically criticized what he believed were inconsistencies in the Xindi's powers, such as being able to time travel in "Carpenter Street" but being unable to destroy Enterprise. ("The Forgotten" audio commentary, ENT Season 3 Blu-ray special features)
Chris Black believed that, in theory, the concept of introducing a race comprised of multiple species was one of numerous facets of the Xindi arc which sounded "great," though he had problems with the execution of the arc generally. (In a Time of War, Part One: Call to Arms, ENT Season 3 Blu-ray special features) He remarked, "Love or hate the Xindi mythology and arc, there was some pretty nice makeup on those guys [...] The fact that they refer to each other by their species designation [...] – that they don't have names or self-identify in some way, that they just refer to each other as 'Humanoids' or 'Reptilians' or 'Insectoids' – is a little weird but maybe that's just the universal translator." Executive Story Editor André Bormanis concurred with these statements. He said about the Xindi make-up, "That was pretty incredible," and, after laughing at Black's observation regarding how the Xindi address one another, he admitted that these oddities "could be" due to the universal translator being faulty. Bormanis also liked the fact the Xindi involved five intelligent species, of which he said, "I always thought [it] was a very cool idea." ("Countdown" audio commentary, ENT Season 3 Blu-ray special features) He also pointed out that this example of an alien race is more akin to the variety of intelligent lifeforms on Earth than the idea of each planet having merely one technological, intelligent species. (In a Time of War, Part Three: Final Conflict, ENT Season 3 Blu-ray special features)
However, some writing staffers have voiced suggestions as to how the Xindi could have been portrayed differently. David A. Goodman thought they should have featured more visual effects than they actually did. He opined, "The better thing to do would have been to have, you know, you can't of course do it, but rather than four guys in prosthetics is one guy in prosthetics and three CGI guys." ("The Forgotten" audio commentary, ENT Season 3 Blu-ray special features) Mike Sussman was frustrated that the Xindi were used in the way they were, preferring the Romulans to have been used instead. "No offense to the Xindi, wonderful people, they're not Romulans," Sussman critiqued, with a chuckle. (In a Time of War, Part One: Call to Arms, ENT Season 3 Blu-ray special features)
Those who approved of the Xindi included visual effects artists. Character Animator Sean Scott referred to the Xindi as having been "an exciting addition" to the series. John Eaves remarked, "The Xindi were a very fun race to draw for."  Dan Curry was pleased with how realistic the CG Xindi turned out. (Star Trek: Communicator issue 149, p. 50)
Even several actors thought highly of the Xindi. At one time, Archer actor Scott Bakula remarked positively about the Aquatics, Reptilians, and Arboreals. He went on to say, "There's something wonderfully complex about the whole Xindi situation and the various species and their own in-fighting racial issues, that [...] is relevant and makes for great storytelling." (Star Trek Magazine issue 113, p. 7) Jannar actor Rick Worthy loved the Xindi. (Star Trek Magazine Special 2016, p. 109) He commented, "I loved that the Xindi all looked different [....] The Xindi were a great nemesis for Star Trek: Enterprise."  Worthy further explained that "what [he] found interesting" about the Xindi was that, whereas the Arboreals were established as having a fear of water, other Xindi resided in water, and yet others lived on the ground, even though they all belonged to the same race.  Trip actor Connor Trinneer opined that the Xindi were "clearly a [...] not too veiled reference to terrorists." (In a Time of War, Part Two: Front Lines, ENT Season 3 Blu-ray special features) Phlox actor John Billingsley highly approved of the Xindi in concept but didn't think they, particularly the Insectoids, were made to look scary enough, due to how limited Star Trek: Enterprise's budgets were. "For me, that was the problem with the Xindi arc, was, you know, was the Xindi," he laughed. "I like the actors. It's not no slam on the actors." (In a Time of War, Part Three: Final Conflict, ENT Season 3 Blu-ray special features)
Despite proving relatively popular, the Xindi were – following their many appearances in the third season – intentionally excluded from appearing as regularly, thereafter. Between the airing of the third and fourth seasons, Brannon Braga declared, "At this particular instant, I never want to see another Xindi again. That's not to say they might not make a return. They're certainly a fun species to deal with. But at this point, I have to believe people will have had their fill." (Star Trek: Communicator issue 151, p. 35)
While the Xindi have not appeared explicitly in the novels, the novel Armageddon's Arrow features the crew of the Enterprise-E comparing their current situation to the Xindi attack, as both feature an alien race attempting a pre-emptive attack on another race (although the Enterprise-E crew are unaware of the time travel element of the Xindi crisis, despite rumours that time travel was involved).
In Star Trek Online, by the year 2410, the Xindi have been a long-time member of the Federation, though rarely seen in Federation space due to a long period of self-exile in the Delphic Expanse. Following the discovery of the Solanae Dyson Sphere in the Delta Quadrant and the revelation of Iconian manipulation of galactic events, the Xindi emerged from their exile and contributed ships and personnel to various Alpha and Beta Quadrant powers, including Starfleet, the Klingon Defense Force and the Romulan Republic.