Exitar

Exitar the Exterminator is a powerful and ancient cosmic entity within the landscape of Marvel comics, a member of the godlike race known as the Celestials and their appointed executioner of worlds and races deemed "failures" to the Celestials.

Exitar is thus one of the most fearsome, dreadful and dangerous of the many Celestials - though he is not, despite his great destructive might, fully malevolent.. much like Galactus and his fellow Celestials he is performing a cosmic duty, though it can be seen as immoral to mortal beings, since to a cosmic entity such as Exitar the genocide of entire species is completely justified.

Exitar bares to malice to those he is summoned to destroy, nor does he mourn their passing - to Exitar it is all part of a cosmic duty and thus his arrival is usually a sign of the "end days" for whatever unfortunate world the Celestials have judged "impure".