Spoiler alert! John Wayne made sure the ending of his last film, The Shootist, was to his liking.
His character, the dying gunfighter J.B. Books, takes on three gunmen in a saloon, killing them all—before a barkeep shoots him in the back. Young Gillom Rogers, who idolizes Books (and is played by Ron Howard), then kills the bartender before throwing the pistol away in disgust.
But in the original script (and book), Gillom is the one who shoots Books. The Duke hated that morally ambiguous take—the new killing off the old—and the story was changed.