Anuxa was a pre-Marvel comics character featuring in Tales to Astonish, 1960 - this makes him one of Marvel's earlier supervillains since the "official" Marvel age is not usually seen to begin until after the release of the first Fantastic Four comic (which sparked the "modern age" of Marvel canon).
Like all characters and events in the "pre-Marvel" comics Anuxa is not canon in the current Marvel universe but is also not completely eliminated from said canon - rather he can be considered "in limbo" until writers or events within the "mainstream" Marvel universe counter his existence one way or the other.
Anuxa is a scout for an advanced alien species of immense strength, size and telepathic powers - a million years before the current era (as of 1960) Anuxa was sent to Earth and told to wait for the extinction of its dominant species before claiming the planet as his own.
Anuxa watched the extinction of the dinosaurs and the Neanderthals but grew increasingly frustrated that despite their frequent warring the human race simply would not wipe itself out, eventually, when humanity created the first nuclear bombs Anuxa became delighted - finally seeing a means by which humans could wipe their species out for good.
Anuxa would later be awakened by a nuclear sub and its skipper, whom it shared its history with and bragged that it would soon be victorious as mankind would wipe itself out via nuclear weapons, it then disappeared back into the glacier which it was lurking in - presumably it remains there to this day, waiting for humanity to destroy itself.
- the dinosaurs in the real world went extinct long before "one million years ago" - this can be seen as an error by writers or hyperbole by Anuxa, who was already established as a very arrogant and malicious entity.
- Anuxa is a warning against nuclear weaponry, a common theme in many stories of the time.
- Anuxa is unique among Marvel's many alien invaders in its takes a largely "pacifist" approach to destroying humanity, opting to observe events from afar and confident that mankind shall destroy itself without his aid : this makes Anuxa one of the more striking examples of a "hidden" threat (which, sadly, is unlikely to be revisited in modern Marvel)