In two specific separate scenes Ledger improved some of the most memorable moments in cinema.

When Gordon is promoted, the unscripted yet darkly humorous clapping the Joker does in his cell is one such instance. Director Christopher Nolan informed the crew to continue filming and as we all know, it made it into the film and is definitely remembered.

Another instance is when Ledger is leaving the hospital rigged with explosives. He is walking outside headed towards the bus to make a getaway and stops to fidget with the remote. It was yet another unscripted part of the film, but one Ledger played off flawlessly.

I don’t think enough credit is given to improv actors. Have you see the show Whose Line is it Anyway? My god, Wayne Brady is absolutely hilarious! It takes enormous talent to answer quickly on your toes, or in Ledger’s case, do what feels natural to you in character that adds so much to a movie.