When Heath Ledger was preparing to play the Joker in The Dark Knight, he locked himself in a hotel room for a month and put together a diary of inspirations for the role. Here's a tantalizing glimpse at that diary, from a French documentary.

The above clip comes from a documentary called Too Young To Die, and that's Ledger's father Kim speaking and showing off the diary. According to the Youtube poster, here's what Kim Ledger is saying (under the dubbing):

This is the Joker's diary.

In order to inhabit his character, he (Heath) locked himself up in a hotel room for weeks.

He would do that. He liked to dive into his characters, but this time he really took it up a notch."

"The hospital scene is interesting because when he was a kid, his sister Kate liked to dress him up as a nurse. He was really funny like that. He also was in the movie.

This is a make-up test which was done eight months before. Before the end of the shooting he wrote "bye bye" on the back of the page. It was hard to see this.'

It only makes you appreciate Ledger's intense performance more, to see all of the inspirations he drew on to put it together. There's so much weird imagery in that book. [Comic Book Movie]