Dormammu

A classic Doctor Strange villain, Dormammu is the ruler/dictator of the Dark Dimension. Before clashing with Strange, he has managed to conquer multiple dimensions and universes, merging them with his own. An absolute dictator, he had no interest in the fact that these assimilations broke apart the conquered territories.

But, despite being called pure evil and despite being one of the ultimate Marvel supervillains, he also has some other traits, such as staying true to his own principles and demonstrating nobility in some situations. Thus, despite desiring to conquer Earth, he leaves the planet alone "“ just because he made a deal with Strange to defend his own domain against attacks. He respected his promise and never attacked Earth on purpose. As far as his nobility is concerned, he went as far as scolding Baron Mordo when the latter intervened in a duel with Doctor Strange.

Dormammu has a vast array of powers, ranging from necromancy to time travel. But his greatest one is his mystical power. He is, after all, considered one of the strongest magic users in the Marvel comic book universe "“ according to himself (which doesn't say too much, since he is pretty narcissistic), he is on par with Odin, one of the most powerful characters in the Marvel universe.

Dormammu cannot be killed, since he will instantly reform in his own Dark Dimension. He is so powerful that, at one time, he managed to kill Doctor Strange (as the Ancient One), that latter being aided by the Guardians of the Galaxy and the Phoenix Force. His defeat, at that time, was just his banishment to his home dimension.