8. Christian Bale
You only have to look at the above image to appreciate the lengths that Christian Bale will go to in order to successfully carry out an acting role. Such was Bale's determination to diversify, he lost 63 pounds for his role in The Machinist, before gaining 109 pounds for his role in Batman Begins (which was 40 pounds more than director Christopher Nolan actually wanted him to gain, so he then had to drop that amount before filming commenced). Bale has played the mysterious Bruce Wayne in the Dark Knight trilogy, the emaciated insomniac Trevor Reznik in The Machinist, the suave, pretentious investment banker-by-day and psychopathic killer-by-night Patrick Bateman in American Psycho, the drug-addled ex-boxer Dicky Eklund in The Fighter (another role for which he had to lose a considerable amount of weight) and the determined, battle-hardened leader of the resistance John Connor in Terminator Salvation, proving to all that he has huge versatility.