This is the right answer, see 'My Left Foot', then compare it with his later role (Butcher Bill , Daniel Plainview).

Helps too that he has no "baggage" or real persona in the real world. So many actors are all over the place, doing interviews, tweeting, or otherwise being newsworthy. Daniel Day-Lewis doesn't seem to exist outside his films. Bill the Butcher or Daniel Plainview just seem to be these characters that come from the ether and disappear back into it.