Rather than mention all the great performances Paul Newman gave, I'd like to recall a role he chose to give up.
One of my favorite movies is John Huston's version of Kipling's short story "The Man Who Would Be King." It was in Development Hell for 20 years, going through multiple screenplays. Originally, Huston was going to direct Clark Gable as the majestic Daniel Dravot and Humphrey Bogart as the sly Peachy Carnehan. I'm not sure if the stars were going to attempt English accents, or if they were going to be turned into Canadians in the Indian Army, or what.
Then Bogie died. After his comeback in the "Misfits," Gable wanted to revive the project, so Huston was looking for a new co-star, when Gable had a heart attack and died. In the 1970s, the project got relaunched, with Paul Newman and Robert Redford attached. (I'm guessing with Redford as Danny and Newman as Peachy, but Newman being older and almost as handsome as Redford would have made casting more flexible and/or confusing than with Gable and Bogart, where there was never a doubt who would play which role.) John Huston and his secretary, Gladys Hill, wrote a great fourth script.
From director John Huston's autobiography "An Open Book:"
"I sent the new screenplay to Paul, who called me immediately and said it was one of the best things he'd read, but he'd had second thoughts about the casting of the leads, which at that point were to have been himself and Robert Redford. He said they should be played by two Englishmen. Paul, speaking not as an actor but as someone interested in the improvement of the breed, cast it right there: "For Christ's sake, John, get Connery and Caine!"
Screenwriter William Goldman's book Adventures in the Screen Trade includes a fair amount of malicious gossip about the swelled heads of big stars he'd written for, such as Redford and Dustin Hoffman, but he only had praise for Newman as a human being.