(covers information from an alternate timeline)
In an alternate timeline where the Xindi destroyed Earth, Yerdrin Lek was hired by the Xindi to help find the last colony of Humans. They paid him to follow Doctor Phlox when he left Denobula, which he did in 2165 to treat Jonathan Archer. Lek tailed Phlox to the Ceti Alpha system, and informed the Xindi of its location. He was captured and interrogated by Starfleet officers aboard Enterprise NX-01 (where he tried to pose as a dealer in Rigelian flamegems). However, it was too late and, following his signal, the Xindi attacked Ceti Alpha. Lek presumably died in Enterprise's brig when the ship was destroyed in a subspace implosion which negated this timeline. (ENT: "Twilight")
Yerdrin Lek was played by actor Brett Rickaby.
The final draft script for "Twilight", dated 6 November 2003, gave this character the name of Yerdrin Lek. Earlier drafts called him "Yedrin Koss", but this was changed because there were already two Star Trek characters with similar names: Dax host Yedrin Dax and T'Pol's husband Koss. Promotional materials for the episode used the earlier, incorrect name, which became widely circulated. It is worth noting the character's name was never mentioned in the episode as aired.