Corgman became a necromancer because he couldn't bear losing his family and has raised them... and is looking for a way to restore life. He is actually in the dungeon and the area of the zombies because his undead zombie family got caught up in the migration and he is trying to get them back with the help of his side kick Robina.
His mission "To end the emotional gut wrenching suffering of losing the people we care about. Why? Because it's just not fair."