Christopher Plummer probably remains best-known for his portrayal of Captain Von Trapp in the 1965 blockbuster The Sound of Music. While his character infamously appears rather grumpy on screen, behind the scenes the actor himself was also often in a difficult mood, and despised making the film.

Even in the 1960s, singing nuns and Nazis were somewhat kitsch, but the undeniable charm of Rodgers and Hammerstein’s musical melted the toughest hearts, except perhaps that of its leading man. It’s…