Heath Ledger's Joker bears little resemblance to the prankster played by Jack Nicholson in Tim Burton's 1989 Batman. The Dark Knight is set to take over theatres July 18.

LOS ANGELES -- His sadistic, unhinged turn as the Joker may define Heath Ledger's career, but it didn't drive him towards depression or death.

This from his colleagues, out promoting The Dark Knight while dispelling speculation the disturbing role consumed the late 28-year-old actor.

"Heath, in between takes, would laugh and joke and sit down on the curb and have a cigarette and talk about (his daughter) Matilda," remembers Gary Oldman, who returns as incorruptible cop Jim Gordon in the Batman Begins sequel.

Ledger died in January weeks after completing work on the film, due July 18. The idea he had immersed himself too deeply in the Joker persona came in part from an interview in which he admitted to having trouble sleeping while playing such a remorseless, rampaging sociopath. Ledger was killed by an accidental overdose of prescription medication, including sleeping pills.

"I think everybody wants to go, 'Oh, it was the role that drove him ... ' but you'd have to be neurologically f---ing mental -- you'd have to have a disorder -- to play a part and let it affect you so much that you can't sleep," Oldman says. "People want a darker story than there really is. I don't know if he had substance abuse in the past and people talk about partying and the stuff he used to do, but I was never a witness to that. I worked with a sweet kid who had such a heart. He was lovely guy. I worked with this guy who was completely committed to the role and the work and wanted more than anything to be taken seriously as an actor. He was on time; he knew the lines. He was a nice kid."

Worse, theorizing Ledger struggled to untangle himself from his alter-ego "diminishes his skill as an actor," director Christopher Nolan tells Sun Media. "The job of an actor is to be somebody who takes on a character and distinguishes between real life and the character. Anyone who has spent time on a movie set knows it's a very artificial environment. And the great skill of somebody like Heath Ledger or Christian Bale, all these guys, is that when the camera rolls they can find this great character."

Far removed from the near-comical menace of Jack Nicholson's purple-clad prankster, Ledger's Joker is more terrorist than crook, a scarred, homicidal anarchist who wages a war with Bale's Batman for Gotham City's soul.

"Some men just want to watch the world burn," Michael Caine's loyal butler Alfred warns his body-armour-wearing boss. And burn it does. Easily the most violent and grim of the Batman films, it is a brooding comic-book crime noir, propelled by Ledger's scorching tour de force.

"He was a fierce talent," Bale says of his on-screen nemesis. "Clearly it's tragic that we're talking about this in terms of being his last performance. I would love it if he was walking in the room right now; he was great company. I looked forward to working with him many more times and looked forward to being his friend for many years to come. But this movie can be a celebration of his talent."

Says Oldman, "Certain actors go along -- really good actors as Heath was -- they go along and have careers and travel at subsonic speed and occasionally break the sound barrier: you can think of people like Jack Nicholson in One Flew Over the Cuckoo's Nest and Al Pacino in Dog Day Afternoon -- there are certain landmark performances where you think they just fly.

"And Heath has done that here. He's just tuning into a radio station, he's got a frequency none of us could hear. It was like he found something. I knew it was special the first day I worked with him. I called a friend and they asked 'How's Heath as the Joker?' and I said, 'He's going to be sensational.' You could tell already. How good he turned out to be is beyond my expectation."

And it's a performance that, Nolan stresses, was not modified or altered following Ledger's death. For example, a scene in which the Joker emerges from a body-bag remains intact.

"I'm very confident that the performance has been edited exactly the way it would have been had Heath not died. It was very important to me that his performance be put out there exactly as he had intended it to be seen."

More Artists