When the war hero-film star Audie Murphy, asked to play the deadly sniper Scorpio in Don Siegel's Dirty Harry, died before giving an answer, Andy Robinson stepped in as Murphy's reluctant replacement. Indeed, Robinson was so anti-gun that he flinched every time he fired. Siegel actually had to shut down production for a week and send his sniper on a crash-course in sniping.
[Nor was Clint Eastwoon Siegel's first choice for Harry Callahan. Frank Sinatra (who hurt his hand in an accident), John Wayne, Steve McQueen and Paul Newman were all approached before Clint took the role.]