The Magister is an alternate version of The Ace of Chaos from the blog Horsemen. He has long brown hair, has a missing eye, and his remaining eye glows. He's a powerful spellcaster, who can supposedly summon doors into Netherworld. After a heated battle with the Gambler, he proved that he really can do this. The incantation for the spell is apparently "Open the f*ck up!", which apparently must be said in just the right way for it to activate.
Magister and the Gambler have been at war with each other over a woman for a long time, and it's revealed through flashback that the Gambler is the one who took the Magister's eye.