Here's a peek at the incredibly detailed diary Heath Ledger kept to play the Joker in 'The Dark Knight'

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Heath Ledger went to extreme lengths to prepare for his Oscar winning performance as the Joker in "The Dark Knight."

The late Heath Ledger won an Oscar for playing the Joker in "The Dark Knight" for good reason. His committed performance brought the iconic comic book to character to life in the most terrifying way imaginable. 

Ledger passed away in January 2008, unfortunately unable to see the remarkable impact his performance had.

A clip from the documentary "Too Young to Die" has surfaced, and it gives a brief glimpse into Ledger's method for immersing himself in the Joker's madness.

This clip reveals the diary Ledger kept as he prepared for the role, which Ledger's father Kim looks through. To prepare to play Batman's greatest foe, Ledger locked himself up in a hotel room and then in his apartment for around a month.

The diary says a lot about both how Ledger felt during those days, as well as his many influences for the part.

In the notebook, an image of a hyena is visible:

Broadview Pictures

Perhaps this inspired his laugh, which often has a hyena-like quality to it:

The notebook is filled with dialogue from the film that Ledger jotted down. He even wrote down all of his dialogue for the entire hospital room scene:

Broadview Pictures

In this scene, Ledger memorably wears a nurse's outfit. In this clip, Kim notes that Heath's sister Kate used to dress him up in a nurse's outfit.

In the notebook, you might notice one figure that constantly pops up:

Broadview Pictures

You can see it again on another page:

Broadview Pictures

That is none other than Alex DeLarge (Malcolm McDowell) of Stanley Kubrick's masterpiece "A Clockwork Orange" from 1971.

Warner Bros via YouTube

Malcolm McDowell as Alex DeLarge in "A Clockwork Orange."

In "A Clockwork Orange," Alex DeLarge is the leader of a gang that inflicts random horrible acts on unsuspecting citizens. Alex rapes, steals, and fights others for the fun of it. He sure does sound a lot like the Joker, a villain who simply wants "to watch the world burn."

Ledger was even able to flawlessly replicate that terrifying expression, often called the "Kubrick Stare."

Warner Bros.

Ledger mastered the art of the "Kubrick Stare."

Watch the full clip below: