Many people today think of Satan as a little red demon with a pointy tail and a pitchfork—but this vision of the devil developed over many centuries and would be foreign to the writers of the Old Testament, where this figure makes his first appearances. The earliest texts that mention the Satan—it is always “the Satan” in the Old Testament—portray him as an agent of Yahweh, serving as an executioner of evildoers. But over the course of time, the Satan came to be regarded more as God’s enem...