Did Heath Ledger's commitment to his craft come back to haunt him?

The release of "The Dark Knight" - and the critical raves regarding Heath Ledger's portrayal of the Joker - brings to mind a comment made by Jack Nicholson, who originally played the role in the 1989 movie version of "Batman."

The New York Daily News reported that Ledger thought that landing the demanding role was a dream come true, but Nicholson allegedly warned him that the role could take a dangerous toll.

Indeed, Nicholson - and who was furious he wasn't consulted about the role - offered a cryptic comment when told Ledger was dead, the newspaper reported.

"Well," he said, "I warned him."

Nicholson may be flashy, brash and outspoken, but his credibility is rarely called into question. Indeed, the comment may point to the physical and mental expense actors suffer when they assume a role that plays to the dark side of their soul.

For method actors, especially, assuming any role that requires using deep emotional energy can have an even larger impact. The acting style requires the person to wrap themselves in a character's personality - sometimes to the point of strangling themselves.

Marlon Brando, in fact, pointed to that issue when he decided to no longer pursue demanding roles after "Last Tango in Paris." After that, he only took easy roles - his performance in the blockbuster "Superman," for instance - that did little to improve his stature but raked in a lot of cash.

Last year, Ledger told reporters he "slept an average of two hours a night" while playing "a psychopathic, mass-murdering, schizophrenic clown with zero empathy," the Daily News reported.

"I couldn't stop thinking. My body was exhausted, and my mind was still going."

Prescription drugs didn't help, he said in the story. Later, they ended his life.