The Legendary Mage is an Undead

Gelis is a human from Earth who traversed to the realm of the undead, inhabiting the body of a skeleton. In the undead world, he was the lowest level of skeleton, and only had half a body. Then, by a stroke of luck, Gelis was summoned by a great archmage and became the archmage's summoned undead. The archmage was astonished to discover Gelis's extraordinary learning ability. With this unparalleled capacity for learning, Gelis rose to become the God of the Undead.