Who is the Devil? What are demons? Where did they come from, why do they exist, and why do they seem to bear so much malice towards humans?

Many cultures posit the existence of fundamental principles of good and evil, and develop narratives about the way these principles have interacted with humans and continue to do so. This book is the story of the medieval Christian approach to these questions. This approach was woven out of disparate traditions retold and reinterpreted through contexts ranging from the late antique Near East to early modern Europe. In fact, it took several centuries and a vast corpus of often polemic writings to establish the following apparently simple narrative.

There was an omnipotent God who was wholly good. This God created ranks of beings who were purely spirit, without bodies—these were angels. Since they were without bodies, angels were sexless. They were also intellective beings who were made privy to the deep truths of creation through direct revelation from God. They were created wholly good, since God the Creator could only create what was wholly good, but they were also endowed with free will, which entailed an ability to choose their actions.

At some point one of the angels, perhaps even the finest angel, decided that he was so extraordinary he had no need to worship and obey God. Instead he would set up his own throne above that of God. He rebelled against God and drew one-third of all the angels to him. These rebellious angels were routed by the archangel Michael and flung down from Heaven, either to the pit of Hell or to a lower atmosphere. Here they lost their perfectly fine spiritual natures and took on a kind of body—not fleshly bodies like those that humans would have, but grosser bodies than they had previously. These were “aery” or “cloudy” (caliginosus) bodies.

The angel who had led the rebellion now became the Devil or Satan, meaning “the Adversary,” and his ranks of disgraced angelic followers became demons. God had in the meantime created humans to be his special companions. Seeing this, and deprived forever of his celestial home, the Devil burned with envy.