Remember the disabled writer, F. Alexander, who lives at HOME in A Clockwork Orange? In a later scene with him, his musclebound assistant Julian is played by Darth Vader himself David Prowse, who was at the height of his bodybuilding involvement. Not only did Prowse have a role in the film, but he had the guts to stand up to Stanley Kubrick, which few actors ever did with the demanding and headstrong director.
Prowse took issue with the scene in which he had to carry the writer and his wheelchair around a corner and to the dinner table in one take. Kubrick, famous for being insistent on doing many takes of each scene in his films, had Prowse worried about the number of times he'd be expected to perform that feat of strength. Prowse approached Kubrick, arguing, "Your name is not 'one-take Kubrick' is it, you see?" Everyone on the set grew silent, thinking that was the premature end of Prowse's work on the film. Kubrick just laughed and told him not to worry. They got the shot in six takes, definitely a conservative effort on Kubrick's part.
Image: Warner Bros.