But perhaps the biggest surprise was Thomas Mitchell. I've seen him turn up in some interesting places recently, such as Only Angels Have Wings (a non-Capra film which starred, huh, Jean Arthur). Mitchell is no doubt best remembered for his role as Uncle Billy in Capra's It's a Wonderful Life.
There he is in the attached picture with Jean Arthur. Although Arthur was in the film as James Stewart's love interest, her character also had a willing suitor in Mitchell's Dizzy Moore.
Mitchell went from playing a rival for Stewart's leading lady to his beloved but addled uncle in just seven years? Wow. And apparently Arthur turned down a chance to star in It's a Wonderful Life. Maybe that was a good idea...