The Duke was in some serials and non-feature length movies that really drove up his numbers, although he was definitely a working actor.
He was hard-working, he did a great job of functioning despite a serious booze problem, kept working after losing a lung I think, and left a decent body of work that still is worth watching for the most part (probably not his portrayal of Genghis Khan, or that flyboy piece he did for Hughes). My favorites of his include the ones with half-hour fistfights. :’) And of course, the showdown scene in “True Grit” remains one of my favorites by anyone.