Bronx born, stocky Italian-American actor who only appeared in a handful of films, yet earned some degree of immortality for his role as the loyal Corleone capo "Peter Clemenza" teaching Al Pacino how to shoot a crooked police captain in the iconic gangster film The Godfather. He was originally a construction company manager, then he gained work with the New Yiddish Theatre, before breaking into film near his thirtieth birthday. However in 1970, in only his fourth film, Castellano received a Best Supporting Actor nomination for his performance in Lovers and Other Strangers and came to the attention of casting agents for The Godfather. After his strong showing as a tough hoodlum in The Godfather, he became somewhat typecast as a screen criminal and appeared in further crime films including Honor Thy Father and Gangster Wars.

He died in December 1988 from a heart attack, aged only 53.
Specialized in playing overweight characters. His normal weight was about 200 pounds, but producers invariably insisted that he gain at least 50 pounds for roles. In the Director's comments on the DVD of The Godfather, Francis Ford Coppola says that Castellano was not in The Godfather: Part II because he wanted to have someone else (of his choosing) write his dialogue. Has played the father of Bruno Kirby, in The Super, and an older version of Bruno Kirby's character, Clemenza, in The Godfather. Was nominated for Broadway's 1969 Tony Award as Best Supporting or Featured Actor (Dramatic) for Lovers and Other Strangers a part he recreated in an Oscar nominated performance in the film version of the same name, Lovers and Other Strangers.