Before filming began, John Wayne had to lose most of the weight he had put on in order to play Rooster Cogburn in True Grit (1969).
John Wayne became good friends during the shoot with Rock Hudson and even joked that he'd rather have been born with Hudson's movie star face than his own.
During filming, John Wayne fell from his horse and fractured three ribs. He couldn't work for almost two weeks. Then he tore a ligament in his shoulder and couldn't use one arm at all. Director Andrew V. McLaglen could only film him from an angle for the rest of the picture. Wayne's only concern, throughout, was not to disappoint his fans, despite being in terrible pain.
John Wayne liked casting himself against tall actors, so when the 6'7" James Arness became unavailable, he helped cast Rock Hudson, who was at least as tall as he. He also wanted someone to play bridge with, and knew that Hudson was a good bridge player.