The Coridanites (also called Coridans, Coridanians or Coridani) are a humanoid race native to the dilithium-rich planet Coridan III, which is located at the edge of Federation space, near the Romulan Star Empire.
Physically, Coridanites are quite similar in appearance to other humanoid races. In diplomatic situations, Coridanites by tradition were required to wear elaborate masks that gave them a distinct appearance. (ENT episodes: "Shadows of P'Jem", "Demons")
In 2155, the Coridanites were poised to join the Coalition of Planets along with Earth, Vulcan, Andoria and Tellar, but a Romulan attack which caused massive damage to the surface of Coridan, forced them to withdraw from the talks. The Coridanites were semi-independent for over a century, before making moves towards being admitted into the United Federation of Planets in 2267. (ENT novel: The Good That Men Do; TOS episode: "Journey to Babel")