for the Joker I locked myself away in a hotel room for six weeks. I just formulated a voice and a posture and found a real psychology behind the Joker. I really put a lot of work into it. And the experience also on a production scale, by the way, is obviously a completely different shoot. Batman is just such a machine. It's huge and I've never worked on anything that big.
“Last week I probably slept an average of two hours a night,” he said. “I couldn’t stop thinking. My body was exhausted, and my mind was still going.” One night he took an Ambien, which failed to work. He took a second one and fell into a stupor, only to wake up an hour later, his mind still racing.
Here too was his Joker diary, which he began compiling four months before filming began. It is filled with images and thoughts helpful to the Joker back story, like a list of things the Joker would find funny. (AIDS is one of them.) Mr. Ledger seemed almost embarrassed that the book had been spotted, as if he had been caught trying to get extra credit in school.
http://www.youtube.com/watch?v=uKa-aDga1fE
http://www.youtube.com/watch?v=z7Fkc0VM31A