4. Robert De Niro - Brazil
The Commitment: To play "air conditioning specialist" Harry Tuttle in Terry Gilliam's Brazil, Bobby De Niro didn't just go to the effort of styling himself to look like a grungy version of Mario. He also studied neurologists performing brain surgery (likening his character's job to neurology) and became obsessed with researching and convincingly recreating the craft of his character, Tuttle's tools and gadgets in the film being his own. De Niro also insisted on 25-30 takes a time.
The Result: The film isn't bad at all, and neither is De Niro, but the actor hardly features here. For what amounts to no more than an extended cameo, De Niro reportedly drove Gilliam nuts with his obsession for detail, his planned time on set doubling as a result of his meticulous method. Gilliam was initially excited to have De Niro in his picture, but eventually "wanted to strangle" the actor, and - for all De Niro's commitment - it's easy to forget he's even in the film.