According to the late actor's co-star Christian Bale, Ledger researched the part by viewing old clips of the band's bassist, who died in 1979.
"Heath's created an anarchic Joker unlike any ever seen before," Bale explained. "He modelled the part on Sid Vicious which made this punk-like character. His Joker is unlike any other Joker seen before. I think it is a classic portrayal of a great villain."
Bale added that he is not surprised by the calls for Ledger to win a posthumous Oscar for his role in the Batman sequel.
He said: "Heath immersed himself in the role. I would love to see him get an award."
Ledger died in January following an accidental overdose of prescription drugs.