Joker

The Joker was a psychotic anarchist, nihilist, and criminal mastermind (self-professed “agent of chaos”) who rose to power in the criminal underworld by thrusting Gotham City into turmoil, and drew Batman ever closer to crossing the line between hero and vigilante. Heath Ledger, the actor who portrayed The Joker, described him as a “psychopathic, mass murdering, schizophrenic clown with zero empathy”.

Joker Wiki