Azazel was a powerful demon and a Prince of Hell who served Lucifer. Until Sin City, Azazel's name was not revealed and he was referred to by nicknames such as The Demon, The Yellow-Eyed Demon, or Yellow Eyes.
Azazel is a Yellow-Eyed Demon, one of the Generals of Hell commanding the demon army, and seemingly the only one still active by 2007. He was the first supernatural creature and the first demon who appeared in the series.
Azazel (/əˈzəzɛl/) (Hebrew: עֲזָאזֵל, translit. ʿAzazel; Arabic: عزازيل, translit. ʿAzāzīl) appears in the Bible in association with the scapegoat rite. In some traditions of Judaism, Christianity, and Islam, it is the name for a demon.