Thanos

Thanos is a cosmic-level super-villain and a mutant member of the Titan Eternal subspecies with deviant traits. Displaying godlike abilities in numerous attempts to either conquer or destroy reality, his many evil deeds earning him the title of the "Mad Titan".

History
For a long time, Thanos was a nihilist who sought to court Death itself and when he gained the power of the Infinity Gauntlet he became a malevolent God who wiped out a full half of the Marvel universe and waged war with its Cosmic Abstracts.

Earth-199999
This version of Thanos wasn't so much killing, simply out of nihilism, but rather a well-intentioned extremist trying to prevent overpopulation of the universe and the depletion of its resources.

Appearance
Thanos is a giant humanoid alien whose skin was completely purple. He wears golden helmet, golden alien armor, golden boots and a blue suit.