Robin Williams in Good Will Hunting, or most any role he had.

Val Kilmer as Doc Holliday in Tombstone.

Kathy Bates as Annie Wilkes in 1990 film adaptation of Stephen King's 1987 novel "Misery".

mohksinats:
Just rewatched this at the local theater recently, and she is the reason that film holds up to this day.

Had a guy s**t himself because he got sick the morning of the interview and was giving it his all. Helped him with onsite gym to clean up and had his wife come get him. Interviewed him a week later out of pity and he showed up and was hired on the spot. He got my job when I left the company a few years later.