A new German documentary about the life of the late Heath Ledger gives a glimpse into the dairy he wrote as he prepared for his role as the Joker in "The Dark Knight." A scene from the documentary showed Ledger's father, Kim Ledger, as he flipped through the dairy his son was keeping as he tried to get into character as the villain, according to Entertainment Weekly.

To prepare for the role as the Joker, Ledger stayed in a hotel room for more than a month as he tried to get into the head of Batman's nemesis. "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," Kim Ledger said in the clip. "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 was filled with images of different versions of the Joker from the comic books, playing cards, clowns and pictures of Alex DeLarge, the main character from "A Clockwork Orange." There were also a few pages of his dialogue from "The Dark Knight" when the Joker met Harvey Dent at Gotham General Hospital, according to Superhero Hype.

Ledger was posthumously awarded the Academy Award for Best Supporting Actor for his role as the Joker. Ledger died in January 2008 at the age of 28 from an accidental drug overdose of prescription medications including painkillers, anti-anxiety drugs and sleeping pills, according to CNN. His family accepted his Oscar Award on his behalf. Watch the clip from the documentary below.