DANIEL DAY LEWIS (Madness for movies)

• The Boxer (1997): DDL crudely tattooed his hands and trained as a real fighter, twice a day, seven days a week, for nearly three years. His trainer -– the former world boxing champion Barry McGuigan -– remarked that he could have turned professional.
• In the Name of the Father: He slept in an abandoned jail and ate only prison rations.
• The Crucible (1996): He lived in the film set's replica village without electricity or running water and built his character's house with 17th-century tools.
• Gangs of New York: This was the film in which DDL's preparation attracted the most attention. He trained as a butcher, caught pneumonia while on set (having refused to change his threadbare coat for a warmer one because it hadn't existed in the 19th century), and wandered about Rome (where Gangs was filmed) in character, fighting strangers. "I had to do my preparation," he says with a grin. "And I will admit that I went mad, totally mad. I remembered the days of fighting on the Millwall terraces and they stood me in good stead for Bill the Butcher. He was a bit of a punk, a marvelous character and a joy to be – but not so good for my physical or mental health."
• Last of the Mohicans (1992): DDL prepared for the role of James Fenimore Cooper's 18th-century hero Hawkeye by living off the land for six months, learning how to hunt, fish and skin animals.

Gangs of New York (2002) : For playing Bill the Butcher, he flew a butcher from Peckham, South London to America to instruct him in carving up carcasses. He also hired circus performers to teach him to throw knives, and he came down with pneumonia during shooting because he refused to change his threadbare woollen coat for a warmer one on the grounds that as a poor 19th century New Yorker, he wouldn’t have owned a thick coat. 

Also while on set, he obsessively listened to foul language songs of rapper Eminem in a bid to keep up his "level of aggression". His preparation for the role was so intense that other actors were reportedly scared of him around the set.

His excessive preparation & immersion in the skin of his character irked Liam Nesson when DDL insisted on being addressed by his character's name when they met at the gym of their hotel. 

From the Guardian:

"To portray Christy Brown, the Irish artist who suffered from cerebral palsy and was only able to control his left foot, Daniel Day-Lewis asked to be wheeled around the set in his wheelchair, and crew members were required to spoonfeed him and lift him around. He damaged two ribs during filming from hunching in his wheelchair for weeks on end. He taught himself to paint using a knife held between his toes, and studied disabled patients at Sandymount School and Clinic in Dublin. Day-Lewis won a Best Actor Oscar.