A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard's downfall, he used the wizard's body as a springboard to gain influence and power in his new world.
"This is impossible," one of the mages stammered. "People who know how to do this kind of magic are long dead."
Not everyone agreed with his comment, however. Necromancers were very hard to kill, and despite the numerous attempts to eliminate necromancers, they thrived. There were always a few necromancers that would hide away and recover in some remote corner of the world. When there were enough believers in their religion, there would be another attempt at eliminating necromancers. Every time, the Church of Light would announce that they had eliminated all evil, but it was never the truth. Everyone had forgiven this, however, because it was better to have the Church in charge than the necromancers.