Heath Ledger Kept a Diary While Playing Joker for 'The Dark Knight'

Several years after his death, Heath Ledger's last performance as the Joker in "The Dark Knight" is still being buzzed about, and now a German documentary about his life revealed a diary that helped the actor get in touch with his inner villain.

One particular scene from the documentary showed Ledger's father, Kim Ledger leafing through a diary that his son kept while preparing for the role, according to Entertainment Weekly.

"He pretty well locked himself up in a hotel, in his apartment, for a month or so, to sort of galvanize the upcoming character in his own mind," his father said. "That was typical of Heath on any movie. He would certainly immerse himself in the upcoming character. I think this was just a whole new level."

The diary is filled with drawings, scribbles, and even photos. There are images of playing cards, scenes from "Batman" comics, photos of hyenas, and even stills of Alex DeLearge from "A Clockwork Orange."

In one page, the word "Chaos" is written in all caps and highlighted in the color green.

Ledger was only 28 years old when he died in January 2008. "The Dark Knight" was shown months after his death and he received a posthumous Oscar award for his role as the Joker.

Throughout his lifetime, the young actor appeared in several movies such as "Brokeback Mountain," "A Knight's Tale," "The Patriot," and even the chick flick "10 Things I Hate About You."

His "Brokeback Mountain" co-star Jake Gyllenhaal said that Ledger's loss actually made him re-think his life and career, adding that it was "unfortunate" that Ledger left the world sooner than expected.

"He was incredibly special and that doesn't even come close to encapsulating who he is, who he was," he said.

Gyllenhaal developed a really good relationship with Ledger on set and he is more determined than ever to forge stronger ones now.

"I'm trying to have relationships that are as real as they possibly can be on a movie set, be close to people because I know that it's precious," he said. "And I know, not only can this career end in a very short period of time and this or that can happen, but that life is precious. I think losing Heath and being a part of a family that was something like the movie, the movie we all made together, makes you see that, makes you appreciate that and hopefully moves you away from the things that really don't matter to the things that do."