John Wayne appeared with Duke in a series of B movie westerns in 1932-33 and both seemed to get equal billing in at least six movies.
Duke was a true wonder horse.
In RIDE HIM, COWBOY, John Wayne proves Duke was not a killer by riding him and the horse seemed to take to him immediately.
After trying to buck him of course. He established himself as Wayne’s ride by, in one scene, unsaddling Wayne’s black horse with just his teeth and running the mount off.
In these six movies, Duke did all sorts of tricks, usually involving pulling up trees or posts he’s tied to to race to the rescue. Wayne was a different character in each movie, always John with new surnames, but the Wonder Horse was forever Duke.
One thing I discovered was that John Wayne was not particularly fond of horses. To him, they were just tools of the trade in making cowboy pictures.