The Joker is a fictional character who appears in Christopher Nolan's 2008 superhero film The Dark Knight, based upon the DC Comics character and supervillain of the same name. He was played by Australian actor Heath Ledger. A psychopathic criminal mastermind and mass murderer with a warped, sadistic sense of humor, the Joker is hired by Gotham City's mob bosses to kill the vigilante Batman (Christian Bale), and also comes into conflict with Batman's allies, Gotham police officer James Gordon (Gary Oldman) and district attorney Harvey Dent (Aaron Eckhart). The character embodies themes of chaos, anarchy and obsession: throughout the film, he expresses a desire to upset the social order in Gotham through crime, and defines himself by his conflict with Batman.
Ledger's interpretation of the character is specifically influenced by the graphic novels Batman: The Killing Joke and Arkham Asylum: A Serious House on Serious Earth. In the film, he wears the character's traditional purple and green color palette, while his facial appearance includes clown makeup that covers facial scars of a Glasgow smile, and green hair. The character also explores techniques found in Ledger's previous performances, including his clown act in Terry Gilliam's fantasy film The Brothers Grimm, while also referencing paintings by artist Francis Bacon, Anthony Burgess' novel A Clockwork Orange and various punk rock musicians. Ledger's casting as the Joker was initially controversial.
The Joker is considered Ledger's finest performance; he himself regarded it as his most enjoyable. When the film was released in July 2008, six months after the actor had died from an accidental prescription drug overdose, the performance caused a sensation, receiving widespread acclaim and numerous posthumous accolades, including the Academy Award for Best Supporting Actor.