Belzebub

Beelzebub is a fallen angel, who was over confident of it's abilities and went against god, it's punishment was to be cast into hell where he turned into a demon. It seems to be power hungry, litterally. It eats the abilities of power users. Heike reveals in chapter 138 that as one of the founders of Eden, he was the one who took away Ogami's ability to control Beelzebub, in the form as a giant feather. Beelzebub's true form is the achromatic flame of purgatory, Seraphim, the six winged angel.