Captain Sera Vaun was a Starfleet officer, qualified doctor, and the first commanding officer of the USS Calhoun. She died during its inaugural flight in 2390, while removing a brain parasite from her first officer, Commander Fox D. Main. The parasite attempted to transfer to Vaun, killing her. (Frontier Fleet)
Commander Main succeeded her as the Calhoun's second commanding officer.
Sera Vaun first appeared in episode 1x01, "Into the Unknown". She died in episode 1x03, "Main's Brain". She would appear again, briefly, in episode 1x16 "Shadows of Time" (her last appearance to date), when the crew of 2390 was brought into contact with the crews of three periods from the Calhoun's future.
Almost all archive material regarding Sera Vaun has been lost, as the Frontier Fleet website was entirely redone several months after the character's death. Her character biography has thus not been preserved, and neither have the posts in which she appeared. Her very brief appearance in episode 16 has, however, been archived.