Okay, anybody who says that Daniel Day-Lewis's performance was not that good, please stand up. Bill the Butcher'll plunge a knife through your heart.
To qualify into the Acting Hall of Fame, three conditions must be satisfied. First, the actor should become the character. And in this film, did the actor become the character? In this case, why the answer is yes. As with any Daniel Day-Lewis film, he totally becomes the character, on and off camera. Daniel Day-Lewis is in fact well-known for his acting eccentricities, staying in character as long as production is in progress, even if the cameras have stopped rolling. It was reported that he even had a bout of pneumonia during filming, and he stubbornly refused to be treated, saying it wasn't staying true to the period. I think he was finally persuaded when someone pointed out that during the period, people actually died of pneumonia.
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And finally, the third condition that must be satisfied is that no other actor should be able to play the part better. The role must be tailor-made for that specific actor. This doesn't mean that only Daniel Day-Lewis can play Bill the Butcher. That would be an insult to all the other brilliant actors in the Hall of Fame. Perhaps the correct way to say it would be that only Daniel Day-Lewis can play Bill the Butcher the way he did. The level of artistry and devotion to the craft is unparalleled with this actor, which is why Daniel Day-Lewis, despite his considerably shorter filmography compared to other actors, still remains one of the most respected thespians of his generation.