Azazel was king of the seirim, an ancient speceies of goat-like spirits. Although some say "Azazel" was simply the name of a place near Jerusalem, other say that it refered to an archdemon who dwelled in the desert. In ancient Jewish custom on the Day of Atonement, two goats were brought to the tabernacle. One goat was sacrificed for Yahweh, the other was laden with the sins of the people and taken to the wilderness for Azazel. He is spoken of in Leviticus 16:8:
And Aaron shall cast lots upon the two goats; one for the Lord, and the other for Azazel. And Aaron shall bring the goat upon which the Lord's lot fell and offer him for a sin offering. But the goat on which the lot fell for Azazel, shall be presented alive before the Lord, to make atonement with him and to let him go to Azazel in the desert.
As this passage shows, Azazel was an imporant in ancient Judasim as Satan came to be in Christianity. Azazel represented the powerful evil supernatural adversary to the Lord. Azazel appears in the Apocryphal Book of Enoch as an angel fallen from heaven becasue he lusted after mortal women. One earth he then established himself as a corrupt archdemon teaching unrighteousness. In the Book of Enoch he is charged with revealing eternal secrets to humankind. God responds to this charge by sending angels to bind Azazel and imprison him in the desert in a place called Dudael. He is to remain there until the Final Judgement.
In Islamic lord, Azazel is also mentioned as a fallen angel who lusted after mortal maidens. His name becomes interchangebale with Iblis and then Iblis becomes the archdemon of Islamic lore.