“In preparation for his role as The Joker, Heath Ledger hid away in a motel room for about six weeks. During this extended stay of seclusion, Ledger delved deep into the psychology of the character. He devoted himself to developing The Joker’s every tic, namely the voice and that sadistic-sounding laugh (for the voice, Ledger’s goal was to create a tone that didn’t echo the work Jack Nicholson did in his 1989 performance as the Joker). Ledger’s interpretation of The Joker’s appearance was primarily based on the chaotic, disheveled look of punk rocker Sid Vicious combined with the psychotic mannerisms of Malcolm McDowell’s character, Alex De Large, from A Clockwork Orange (1971).”

Text Source IMDB