Dark lord
In his Christian science-fiction novel Out of the Silent Planet, C.S. Lewis had each planet be ruled by an alien space angel called an Oyarsa who was sent there by Maleldil son of the Old One. But the Oyarsa of Earth tried to start a rebellion against Maleldil so he was banished to Earth and while there tried to make everyone evil to destroy Maleldil’s laws so Maleldil came to Earth and became human to stop the Fallen Oyarsa to the point where Maleldil died to save the world from him. In the sequel Perleandra, the narrator calls the Fallen Oyarsa the “Dark Lord of the Silent World” and the Fallen Oyarsa turns out to be The Devil.