Mangog

Mangog is a monster found in the Marvel comic book multiverse, most prominently featured in the works concerning Thor, having its origins as one of the myriad threats predating Thor and being brought into existence due to the actions of a younger Odin.

History
Mangog was the result of a truly horrific mass-murder performed by Odin that resulted in the deaths of a "billion billion" lives, the combined hatred of which would live on as the demonic destroyer known as Mangog, who sought to destroy Odin as well as the Asgardians as a whole. Due to being a creature of pure hatred, it also sought to feed on and consume negative emotions as a whole and thus naturally slaughters everything it comes across once awoken.

Without negativity to feed on, Mangog will inevitably weaken and shrink to near-nothingness, but at its peak is a being so powerful, it can easily overpower multiple Asgardians and similar deity-class entities.