John Hartford's "Gentle On My Mind" is often associated with Glen Campbell, who scored a mammoth hit with it, and used it as the opening theme to his CBS variety show.
In 1969, actor Dale Robertson, at the time the host of Death Valley Days, took a turn as a country crooner on The Johnny Cash Show, performing a cover of "Gentle". Like, who knew?
Robertson's previous series, Iron Horse, ran for 2 seasons (1966-8), and came from the same studio that packaged Cash's variety show---Screen Gems. Small world, eh?