Daniel Day-Lewis took his preparation for Gangs of New York (2002) to extremes that put his own health at risk. To play Bill the Butcher, he didn’t settle for memorizing the script: he learned to work in a butcher shop, practiced knife-throwing, and trained until he could touch his character’s prosthetic eye with the tip of a blade without blinking.
His transformation didn’t end when the cameras stopped rolling. He maintained the villain’s accent and intimidating personality, even during meals. Leonardo DiCaprio said he practically didn’t speak to the actor out of character for months.
But his most extreme decision came in the cold. He refused to wear a modern coat because his character lived in the 19th century. He ended up coming down with pneumonia and, according to accounts from the set, initially refused medication for the same reason. He eventually agreed to receive treatment.
During a fight scene, he also suffered a broken nose and kept acting.
For Day-Lewis, playing the Butcher meant living as he did, even when that commitment was no longer safe.