Jack Nicholson — Almost Michael Corleone

Francis Ford Coppola considered Nicholson for Michael Corleone in The Godfather before the studio pushed for and ultimately cast Al Pacino. Nicholson has said he felt the role should go to an Italian-American actor — a remarkably selfless take for 1970s Hollywood. The Godfather grossed $245 million (over $1.5 billion adjusted for inflation) and made Pacino a legend. Nicholson went on to win three Oscars anyway, so it's hard to call this a regret. But Nicholson as the quiet, calculating Michael Corleone? That's the greatest "what if" in film history, and both actors know it.