Lawrence Olivier as Don Corleone? It almost happened. Open Culture explains:
During casting, Paramount executives originally pushed for Laurence Olivier. But when he couldn’t take the film, and when the director, Francis Ford Coppola, asked them to consider Brando, they initially responded: “Marlon Brando will never appear in this motion picture.” Below, Coppola and co-star James Caan explain how the execs were eventually cajoled into changing their minds, and how film history fell into place. As you watch this, also keep in mind that Paramount originally asked two other directors to make The Godfather before approaching Coppola, and they later wanted Robert Redford or Ryan O’Neal to play Michael Corleone. But Coppola, who threatened to quit production, eventually got his way and put the relatively unknown Al Pacino into the film.
Lawrence Olivier was many magnificent things, but his stabs at tackling accents could be as dangerously helter-skelter as asking Norman Bates to scrub your back in the shower.