William “Bill the Butcher” Cutting (Daniel Day-Lewis) was one of the main character in The Gangs of New York. Per Wikipedia, his real name was William Poole. He was a member of the New York City gang, the Bowery Boys, a bare-knuckle boxer and a leader of the Know Nothing political movement.
Know Nothing or the Native American party was popular in New York City and it was the result of large number of immigrants. Bill and his gang were against and hating 
Irish-Catholic immigrants. Their cheap labor competed for their jobs. Bill used street gangs to play an important role in the political system.