Eldmed Ditigeon

Eldmed is a great demon who reigned during the Mythical Age as the Blaze Death King. He is the new homeroom teacher of Anos' class and one of the Four Evil Kings. Eldmed is a rather bold and cocky man who looks down on his enemies but praises those who are worth praising, due to his unordinary fixation on powerful beings, he is considered both insane and creepy by those who aren't his subordinates, as his twisted obsessions tend to last for millennia. During the Mythical Age, Eldmed became prominent as one of the era's most powerful demons and as one of the Four Evil Kings. While battling for control over Dilhade, Eldmed crossed paths with the Demon King Anos and was defeated. As a result, Eldmed became obsessed with him and wished to see the limits that the Demon King could reach and transcend. He battled Anos numerous times in order to gauge his strength and also set about to create powerful opponents for him. Eldmed screened various human warriors, but only Hero Kanon passed his selection, and even he wasn't a match for the Demon King. (Source: Maou Gakuin Wiki)