Lumiya, born Shira Elan Colla Brie, is a human Imperial agent and self-declared Dark Lady of the Sith. She first appears as Shira Brie in Marvel's Star Wars #56 (February 1982) and returns as Lumiya in Star Wars #88 (October 1984), one of the very few characters the original Marvel run created who outlived it.
The Marvel run's best long game
Brie joins the Rebel Alliance as a pilot, wins Luke Skywalker's trust, and is shot down by him in a dogfight after his own senses tell him she is the enemy. He is right, and nobody believes him, and clearing his name takes issues. Rebuilt as a cyborg afterwards, she returns under a new name with a lightwhip and a grievance.
Legacy of the Force
Two decades of publishing later, the Del Rey novel series Legacy of the Force (2006–2008) brought her back as the hidden Sith Master behind Jacen Solo's fall. That is a substantial promotion for a character created to fill an issue of a licensed comic, and it is the clearest example of the Legends shelf treating the 1980s Marvel run as real continuity rather than an embarrassment.
Continuity note
The Legends timeline places her Sith training under Darth Vader himself, which sits awkwardly beside the Rule of Two — the novels address it by making her a trainee Vader never elevated rather than an apprentice in the doctrinal sense. Readers should treat the lineage claim as contested even within Legends.
Canon status
Star Wars Legends. Neither Shira Brie nor Lumiya exists in current canon.