The mutant superhero known as Rogue started out as a villain.
This was due to her troubled past as a runaway that led her to being raised by Mystique. (Rogue ran away from home when her mutant power first manifested. This was because she was in the middle of her first kiss that caused the boy to go into a coma).
Rogue was a member of the brotherhood of evil mutants under the leadership of Mystique. After permanently absorbing Ms. Marvel’s memories and power due to her mutant power not functioning properly, she reforms and joins the X-men.
Although her backstory is well known, Rogue’s personal information was shrouded in mystery until the Rogue comic series released in Sept 2004. In this series her name is revealed as Ann Marie.
Rogue first appeared in Avengers Annual #10 (1981)