Fallen angel
The Book of Enoch mentions angels who mated with human women. These are supposed to be the same angels mentioned in Genesis. Their children are the giants. According to the Book of Enoch, the giants were slain by the Archangels or died during the Deluge. The fallen angels are imprisoned in the underworld. The most famous fallen angels are named Azazel and Shemyaza. They also teach sorcery and warcraft to humans. Azazel is blamed for corrupting the entire world with his teachings.