Raging Bull (2007), starring Robert De Niro
Robert De Niro was the master of alter egos before Christian Bale and Matthew McConaughey came along. In the film Raging Bull, played by Robert De Niro, the protagonist, an Italian boxer, is gradually worn down by his own destructive actions over the course of several decades. At the time, De Niro’s weight increase of 60 pounds was the largest for any actor playing a part. The effect was dramatic, but it lasted only for the film’s final few scenes and not his everyday life. He had to keep in shape like a boxer for the majority of it. He halted manufacturing and travelled to Italy to stuff himself with pasta. Well, that certainly qualifies as commitment.