Nowadays, when people reference "demons," they don't usually mean a horned gremlin from Hell. But, if you think about it, belief in demons and demonic deities is still very prevalent in our culture. The Exorcist, Buffy the Vampire Slayer, and American Horror Story: Asylum have all featured demons in one form or other. These creatures were pitted against the heroes of the story in a classic battle between and evil. But that's not to say demons are only referenced in fiction. The most sinister of demons aren't on TV or in movies, but in obscure stories from Christianity and other...