Azazel

Azazel is the Governor-General of the fallen angels in High School DxD, a collector of Sacred Gears that he studies. In the anime he first passes himself off as a regular client of Issei, inviting him for drinks or video games, and only reveals himself halfway through the second series. He becomes the club's advisor and a teacher at Kuoh. Sirzechs Lucifer says Azazel dislikes fighting, which is why the fallen angels were first to pull out of the war, and Azazel meets the leaders of the devils and angels to agree a truce.

Fighting Cattleya Leviathan, he cuts off his own arm and replaces it with a prosthetic built from his research. His artificial Sacred Gear seals Fafnir, one of the five Dragon Kings, and can form a Golden Dragon Armor. In Volume 12 he steps down in favour of Shemhazai and becomes Grigori's Advisor of Special Technology. Author Ichiei Ishibumi wrote him as a coach and a "strong and cool explanation character".