Maestro

Bruce Banner from an alternate future timeline. Driven insane by gamma radiation from fallout of a nigh world-ending nuclear war that also made more powerful than ever. Killed a bunch of heroes and kept trophies.

Officially from Earth-9200, several versions of Maestro have managed to meet their end at the hands of a hero from or on Earth-616.

First Appearance

Hulk: Future Imperfect #1 (1992)