Avos Dilhevia

アヴォス・ディルヘヴィア

He is the one who claims to be the Demon King of Tyranny and has brainwashed the demons of the current era. [Spoiler] It is later revealed that Avos Dilhevia is actually Lay Glanzudlii, the reincarnation of hero Kanon. [/Spoiler] (Source: Maou Gakuin Wiki)