Doctor Aspen was a Human who lived in the 23rd century. They had once served as a counselor on Starbase 12, before leaving Starfleet to perform humanitarian aid work at the edge of Federation space.
In 2259, the pirate Captain Angel assumed Aspen's identity for a plot to capture the USS Enterprise and free their lover Sybok. They left the real Aspen stranded on a planet. (SNW: "The Serene Squall")
This character was only mentioned in dialogue.