Necromancer

Idea
A necromancer that wanted more power and fear aging. He modified his soul before making a deal with a demon that would exchange his soul so that he could take control of the demon's body. Once inside the demon he gained the demon's power but the demon wasn't gone, just merged with himself.

Soon his body started to burn with the presence of a soul, third degree burns appeared. Once his body was too damaged to use properly he forced his soul into another demon, merging his soul with his new host.

After enough times forgetting his original name, he took a new one (think of one later)