As a practicing Christian, I think the Bible, where the teachings of my faith reside, defines the unseen reality behind evil as Satan along with the demons (or “angels” in some translations) who follow him. I know this sounds like the stuff of fairy tales, but I think a case can be made that the Bible’s teaching about Satan and the creation account of humankind’s fall in Genesis 3 is as viable an option as any that defines the source of evil in this world.