Trivia: Some of Gene Hackman's scenes were actually filmed with a body double and a voice impersonator. That's because he had already completed all his scenes under Donner's direction and was not obligated to return for Lester's reshoots, either due to unavailability (according to Ilya Salkind) or unwillingness (out of loyalty to Donner). The voice impersonator was also used on a lot of Donner footage for audio consistency.
Trivia: Jack O'Halloran who played Non was a professional boxer between 1966 and 1974. He got as high a ranking as 5th in the world.
Trivia: Actor Jack O'Halloran who played Non had the idea that he should be a mute.