Demon is an Akuma (an evil kind of kami) masquerading in the human realm. He is the former vice-king of Jigoku (Hell) and the founder of Akumakyou (a demoniac religion).

Kogure preached his "religion" as the leader of Seikima-II, a religious group whose aim is to conquer the earth via heavy metal music. In mid-2009 he changed his persona to Demon Kakka ("His Excellency Demon").

(Source: Wikipedia)