This city is ****** up in the head! I can officially give it that diagnosis because I'm a doctor. And cuz I'm ****** up in the head, too.

— Harley Quinn src

Harley Quinn is a criminal psychologist turned flamboyant criminal menace and the former girlfriend and sidekick to the Joker. While her intentions are typically good, her methods often betray her insanity, Quinn has acted as both ally and enemy to Batman.