Zelretch is a Magician, a user of True Magic, who lived for probably thousands of years. He was the one to stop the Aristotele Crimson Moon, also called Type-Moon, from destroying humanity. Crimson Moon heard the planet's will, Gaia, asking for help since it predicted that humans would eentually not need her anymore, so she concluded that humans had to end with her. Zelretch used an ether cannon to draw mana from infinite parallel worlds so that he could push Crimson Moon back when it attempted to send the Moon itself crashing on Earth. Even so, Crimson Moon lost because it never expected a human to have so much power and it also didn't know of the existence of Magic, so it got surprised. Before 'sleeping', Crimson Moon bit Zelretch and made him a Dead Apostle Ancestor. Crimson Moon was the harbinger of vampires and the first ones, the True Ancestors, he created were a 'defensive mechanism' that eliminated everything treathening Earth. Dead Apostle Ancestors were 'spares' and there are 27 of them in the present day, but around half of them were captured by the Church or are reduced in a spiritual state. Zelretch's body weakened after his battle against Type-Moon and now he uses his Magic to travel around other worlds. He occasionally takes an 'apprentice' when going to the Clock Tower, but people see him as troublesome and becoming his pupil may reduce you to insanity. The only reason he isn't hunted by the Church or Clock Tower is because he is too powerful, being amongst the top 10 of Dead Apostle Ancestors. The top 10 are such not because of their power, but due to their special status of being impossible to kill by normal means.