Given my lack of knowledge regarding Southern folklore, I can’t really provide much information about the origins of the “Fool Killer.”
However, the concept of a terrifying apparition that brutally murdered those deemed foolish was potent enough to inspire an O. Henry tale, a Helen Eustis novel that was adapted for a 1965 film starring Anthony Hopkins, and – of course – Steve Gerber’s memorable Marvel Comics villain.
A variation of the Fool Killer myth also bedeviled Quality Comics’ Doll Man in a story that also promotes a “spare the rod, spoil the child” approach to the treatment of mental illness.
Guess there was nothing a severe beating couldn’t cure back in the old days …
From Doll Man Quarterly #23 (Quality Comics, July 1949) , here’s “The Fool Killer Is At Work.” The story is uncredited, but the Grand Comics Database guesses the art is by Iger Studio stalwart Dan Zolnerowich.