For "Dr. Strangelove", Peter Sellers was originally supposed to play four roles in the movie. We've already seen him (as portrayed by Geoffrey Rush in "The Life And Death Of Peter Sellers") as the United States President and as Dr. Strangelove himself. He also appeared as RAF officer Lionel Mandrake, a British observer at the military base where General Jack D. Ripper initiated the nuclear strike on the Soviet Union without authorization. But he was also supposed to play Major T.J. "King" Kong, the pilot of the fighter plane that was able to break through the Russian defenses and drop the bomb on its secondary target.
Here's how Wikipedia describes what happened:
"Ultimately, Peter Sellers played three of the four roles initially written for him. At the start of production, it was expected that he would also play the role of Air Force Major T. J. "King" Kong, the B-52 Stratofortress aircraft commander, but from the beginning, Sellers was reluctant to do so. He felt his workload was too heavy, and he was concerned that he would not be able to reproduce the Texan accent required for the character of Kong. Kubrick pleaded with him, and asked screenwriter Terry Southern (who had been raised in Texas) to record a tape with Kong's lines spoken in the correct accent. Using Southern's tape, Sellers managed to get the accent right, and started shooting the scenes in the airplane. However, Sellers sprained an ankle and could not play the role, as technical constraints would have confined him to the cramped space of the cockpit set."
Veteran cowboy actor Slim Pickens was hired (after the role was turned down by John Wayne and Dan Blocker), and so one of the greatest scenes in movie history was immortalized.
Had Sellers been able to play the role of Kong, he would have been involved in all three areas of activity in the movie, basically being present for our mass destruction on all fronts.
Even though I prefer seeing Slim Pickens in the role, I would have been curious to see Peter Sellers ride out the finale.....
(MAJOR KONG'S MAJOR SPOILER!)