Barbara Kean

Barbara Kean is Jim's on & off fiancee and a secondary antagonist turned anti-heroine in the TV series Gotham. Intending to take over Gotham, Barbara's true colors are revealed in the fifth season in which she reforms and joins Jim Gordon and Bruce Wayne against The Penguin. She is a supporting protagonist until she becomes unstable in the first season, a supporting antagonist in the second season, one of the main antagonists of the third season, a character and major antagonist in the fourth season, and then she finally becomes the tritagonist of the fifth season.

As a villain
At the end of the first season, it is revealed that she is truly mentally unstable, and after an encounter with the dangerous serial killer known as The Ogre, where he tortured, and brainwashed her. It causes her to completely lose her grip on sanity. She is sent to Arkham Asylum but is busted out by Theo Galavan who plans for her to become a member of the Maniax. After Jerome's death, Barbara became rather aggressive towards Jim Gordon and started torturing both him and Lee Thompkins, though she eventually got out of the screen on episode 8 where she fell from the top of the Gotham Cathedral, barely surviving.