This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
The Coridanites or Coridans were a spacefaring humanoid species from the dilithium-rich planet Coridan in the Alpha Quadrant. They have been members of the United Federation of Planets since 2268. (ENT: "Shadows of P'Jem"; DIS: "Magic to Make the Sanest Man Go Mad"; TOS: "Journey to Babel")
In 2151, Coridan had a population of three billion, with the majority living in several cities in the equatorial region. The capital city was surrounded by a shanty town, and there were almost as many bio-signs outside the city as there were within it. The planet was known for having the largest shipyards in its sector, building advanced warp-capable vessels, some of which were rumored to reach warp 7. However, the planet was also embroiled in an internal conflict between the government, backed by the Vulcan High Command, and rebel forces, secretly supported by the Andorian Empire. The Vulcan agenda was to keep the planet's chancellorship stable while the Tau Ceti Accords prohibited any Andorian presence on the planet, which in turn assured Coridan's dilithium exports to Vulcan. (ENT: "Shadows of P'Jem")
Chancellor Kalev invited Captain Jonathan Archer and T'Pol of the NX-class Enterprise to visit the planet, but they were captured by rebels and held for ransom. As a result, a commando force led by Sopek, the Vulcan senior officer of the sector, as well as the Andorian Imperial Guard, led by Shran, who was thereby violating the Tau Ceti Accords, came to assist the rescue. (ENT: "Shadows of P'Jem")
In 2152, Coridanites were represented at an Interspecies Medical Exchange conference on Dekendi III. At one point, the "Coridan Genome Conference" was rescheduled to 1400 hours and changed to auditorium six. This was announced on a speaker system inside the conference building. (ENT: "Stigma")
In 2155, Coridan took part in talks on Earth to form a Coalition of Planets. Here, the Coridanites rejected the Tellarite proposal of a trade embargo against the Orion Syndicate. The Coridan representative emphasized his people's long-standing trade relations with the Orions and claimed that the accusation of Orions attacking Tellarite freighters was slander. (ENT: "Demons")
The Babel Conference in 2268 was to consider whether to allow Coridans admission into the United Federation of Planets. Coridan was considered underpopulated at that time, making the planet susceptible to illegal mining operations, e.g., by the Orions. Federation membership would provide the planet with protection under interstellar law. (TOS: "Journey to Babel"; TAS: "The Pirates of Orion") Mining operations were maintained there by the Orions and Tellarites, among others, a concern that led some to think they should be denied Federation membership. Despite the Orion Syndicate making an initial attempt to sabotage the Babel Conference, Ambassador Sarek of Vulcan spoke in favor of admittance, and was given credit for passage of the measure. Coridan joined the Federation that same year. (TOS: "Journey to Babel"; TNG: "Sarek")
Most Coridanites were humanoids with facial patterns that formed the impression of large scales. A few were bald and had much more extensive scalation. They had blue blood. (ENT: "Shadows of P'Jem", "Demons", DIS: "Far From Home")
ENT: "Demons" drastically changed the appearance of Coridanites from the design seen in "Shadows of P'Jem", their only prior appearance. The design seen in "Shadows of P'Jem" would later make a re-appearance in DIS: "Far From Home" with the characters of Os'ir and Kal.
In the Star Trek: Enterprise "relaunch" novel The Good That Men Do, Coridan (referred to as Coridan Prime) is at the center of a major plot point in the story. The novel also reveals details hereto unresolved by canon productions. The physiological differences between the Coridanites depicted in "Shadows of P'Jem" and those seen in "Demons" is attributed to a special diplomatic headdress worn by those seen in the latter episode. The novel describes the headdress as "a metallic material shaped into the stark features of a humanoid skull" with "overlapping bands of chitinous, lobster-colored fabric" that wraps around the cranium. The overall appearance is said to give the Coridanite a vaguely crustacean appearance.
Taking steps to explain Coridan's 23rd century population issues, the novel depicts 22nd century Coridan as a world rich in resources, on the verge of achieving warp 7, and soon to be allied with the Coalition of Planets. To prevent such advances from spreading to other Coalition of Planets member worlds, the Romulans launch a vicious attack on Coridan, flying a vessel into the planet at maximum warp. Anti-matter from the suicide attackers' ship mixes with Coridan's abundance of dilithium, causing a fireball that spreads across the planet, killing billions. The planet's population is said to be further depleted by civil wars that continue after the Romulan attack.
The reference book The Worlds of the Federation displays a profile of the Coridan system, showing Coridan III as the homeworld of the species, and four more planets as colonies, spreading the population thin over the entire system. Coridanites were frequently targeted for raids by other species and the asteroid belt and ninth planet of the system were illegally mined by the Orions and the Tellarites. A profile picture of a Coridanite male shows them to be Human-like in appearance.