Ledger died in january 2008, just a few months before the release of the movie in July 2008. in the days after his death, some people whether the Joker had killed him. Not literally of course, but they wondered if he could have been "taken over" by the character in some way. jack Nicholson said he knew how demanding the role was from his own experience. When he heard about Ledger's death, he immediately remarked that he had warned Ledger that the role might be dangerous for him.