The film Cat Ballou was directed by Elliot Silverstein from a screenplay adapted by Walter Newman and Frank Pierson from the novel The Ballad of Cat Ballou by Roy Chanslor. Chanslor's novel was a serious Western, and though it was turned into a comedy for the movie, the filmmakers retained some of the story's darker elements.

There is no entry about the novel available on Wikipedia at this time, but here is a link to the film entry.