For every beginning, there is an end. For every Alpha, there is an Omega. I am the Omega.
An evil psycho whose objective is to wipe out every life form from the multiverse. He was once your usual Omega, going to work every 9 in the morning, trying to devise new selection processes. But the strain and responsibility of his job seems to be too much for him, and after centuries of killing thousands of innocent species, he finally cracked. You would to if you're in his position. Imagine, all those years and finally, the two species that survived nearly everything he threw at them, are humans (the idiots) and cockroaches (dood...).
His own body, literally.
He can split a part of the gaseous substance that forms his body and reshape it into a weapon, or an armor, or both.
He is also capable of using magic-like techniques, or at least what seems like magic. It's hard to tell whether he's just using his body or is he really using magic.
He loves to surprise people by materializing in the shadows, or popping up behind them, simply because he thinks it's cool, and cool things are good.
He cracked after thousands of years of killing out weaker creatures so that the best may thrive.
After he cracked, he escaped to the multiverse and became a psychopath that kills for fun.
His only wish is to wipe out every single life form in the multiverse, and will gladly ally with anyone that can remotely advance his plans.