Cain Marko (Earth-5430)

Cain Marko was originally a high-ranking S.H.I.E.L.D. agent, being of prime importance to ensure the organization's success through the years. However, all changed when he stumbled upon the alien entity known as Thanos, which used his body as a vessel in order to regain a physical body. Now Marko isn't himself anymore, but a shell for Thanos, who is bent on universal destruction.