Answer
The answer is Elia Kazan. Strasberg's role in "The Godfather Part II" was initially offered to Kazan, who turned it down. Kazan, a renowned director and actor, had a controversial past due to his cooperation with the House Un-American Activities Committee during the McCarthy era. This association potentially posed difficulties for a project of the scale and prominence of "The Godfather Part II," influencing Kazan's decision to decline the role.