Did you ever hear the story about how he was going to also play a fourth part in Dr. Strangelove - that of Major Kong? He fell off the bomb during filming and broke his leg, so they had to bring in Slim Pickens. Kind of a blessing, actually, as Pickens was pretty damned good in the part.
Since we're on Dt. Strangelove stories:
Stanley Kubrick wanted George C. Scott to go to an extreme for parody. Scott did not want to.
So Kubrick asked him to play it different ways and said he wouldn't use the extreme ones. And then those are the ones he used.
Scott was reportedly furious and refused to work with him again, but they seem to fit the part and movie very well.
I didn't know this, from Wiki:
"During the filming, Kubrick and Scott had different opinions regarding certain scenes, but Kubrick got Scott to conform largely by repeatedly beating him at chess, which they played frequently on the set."