Heath Ledger turned in a truly incredible performance as Joker in 2008's The Dark Knight. So much so that The Academy honored him with a posthumous Oscar after his accidental prescription drug overdose.
Ledger, a method actor, locked himself in a hotel room for weeks, pouring himself into his character in preparation for filming. During this time, he kept a diary.
"It’s a combination of reading all the comic books I could that were relevant to the script and then just closing my eyes and meditating on it," he says. "I sat around in a hotel room in London for about a month, locked myself away, formed a little diary and experimented with voices — it was important to try to find a somewhat iconic voice and laugh. I ended up landing more in the realm of a psychopath — someone with very little to no conscience towards his acts." [Empire]
Now, you can see Ledger's diary thanks to a clip from a German documentary series, Too Young to Die. In an episode of the series, from last year, that focuses on Ledger, the late actor's father flips through the diary next to his son's Best Supporting Actor Oscar.