I know at the time of the Godfather Brando was very established at the time as an great actor. I know Pacino and Keaton only did 2 movies before staring in the Godfather, Caan had done about a dozen before and Duvall was in To Kill a Mockingird and the MASH movie along with more than a dozen others.

My question: What was these legends' status before the Godfather as actors (Caan, Duvall, Keaton and Pacino)?