Nicholson was great, but Ledger was just fucking mind-blowing. A pretty interesting back-story to all this: When informed that Ledger had died, Nicholson cryptically said "I warned him" about the Joker role. Jack Nicholson warned Heath Ledger on 'Joker' role Ledger recently told reporters he "slept an average of two hours a night" while playing "a psychopathic, mass-murdering, schizophrenic clown with zero empathy ... "I couldn't stop thinking. My body was exhausted, and my mind was still going." .