This movie was also known by the alternative title of "Three Were Renegades," the title of the 1937 novel 'Three Were Thoroughbreds' by Kenneth Taylor Perkins, which the film was based, and had been previously filmed as the 1948 film "Relentless."
The idea of putting Clint Eastwood on a scrawny horse in A Fistful of Dollars (1964) came from Tumbleweed (1953), in which Audie Murphy rode a scrawny horse, that is nevertheless very intelligent and saves his life. Sergio Leone loved the idea of a tough wandering gunfighter on a lanky, gaunt horse.
The title of the film, "Tumbleweed", is the name of the horse that Audie Murphy acquires about halfway through the film.
Audie Murphy and Lori Nelson appeared together in another Western, "Destry" (1954).