I'm with those who think his best role (other than as Tom Hagen) was "The Great Santini". He was a mean son-of-a-bitch, but Duvall's portrayal almost makes you like this guy.

His portrayal of Major Frank Burns in "M*A*S*H" was superb, and it showed Duvall's versatility as an actor.

One of his movies that hasn't been mentioned yet is a sleeper, and its kind of charming.... "A Family Thing" (with James Earl Jones) is worth seeing.