In February 2008 actors Johnny Depp, Jude Law, and Colin Farrell signed on to take over Ledger's role, becoming multiple incarnations of his character, Tony, transformed in the "magical" world of the film, in part as a "tribute" to Ledger.

oh, so the movie for which they got 3 other actors to finish production is The Imaginarium of Doctor Parnassus, not the dark knight!