ジーベル
Original host for the magi-crystal curse that summons demons to the planet. Gebel was the only one to survive its effects at such a high level. 
He destroyed the guild that created him, but in doing so realized he was no longer human and had no place on Earth. 
This in turn, lead him to summon the demon castle from hell to appear on the planet.

It is said that his real purpose in summoning the castle was to give Miriam a place of her own, but as his Magi-crystal disease progressed, he soon forgot his own reasoning. 
The more he surrounded himself with hell-spawn, the quicker the magi-crystals engulfed his body. 
He continues to plot the downfall of man, and how to best convince (or use) Miriam to achieve his dark ambition.
gebel (bloodstained)