John Cazale

You may know him as Fredo, Sal, Stan or Stan but in real life John Cazale's too short career consisted of five feature films, everyone of which was nominated for best picture.
The Godfather 1972
The Conversation 1974
The Godfather Part II 1974
Dog Day Afternoon 1975
The Deer Hunter 1978
The astute reader might point out that an Academy Award doesn't mean a damn thing, i.e. Gladiator, Titanic, Rain Man, Platoon, American Beauty, Marisa Tomei etc., but by any standard Cazale's five feature films are classics.
In his final film The Deer Hunter Cazale was dying of bone cancer and Michael Cimino had to shoot around him, when the studio found out they wanted John replaced. Meryl Streep was engaged to John Cazale and she and her fellow actors told the studio they would leave the film if Cazale was removed. The suits did the right thing, probably for the wrong reason.