3. Heath Ledger
Though much has been made of Heath Ledger's performance in The Dark Knight, both in terms of rapturous acclaim and tabloid sensationalisation, there's no doubting that his preparatory period for his turn as The Joker was both extremely dedicated (perhaps too dedicated) and absolutely insane. Ledger's death from an accidental overdose of various medications and sleeping pills shocked the world ahead of the release of Christopher Nolan's much-anticipated superhero opus, and reports soon began to emerge that the actor holed himself up in a hotel room for several months, researching the character, reading up on the effects of insomnia and even writing a journal. He reportedly kept character for most of filming to such a degree that crew members were said to be disturbed by his antics, though the commitment to the role seemed to be well worth it. However, given that Ledger died from ingesting extremely strong sleeping tablets, many began to wonder if his commitment to the role (which he had just wrapped, and was mid-way through shooting The Imaginarium of Doctor Parnassus) may have simply taken too much out of him, and naturally jetting between movie sets is going to make it difficult to sleep, so it would be easy to guzzle down an extra few tablets. Whatever the eventual cause of his demise, there's no doubting that the actor's commitment to the role was astounding and unparalleled for a film of this type and scale. Ledger won a posthumous Best Supporting Actor Oscar, and rightly so.