According to noted occultist and sorcerer Simon Magus, the being was an emissary of a galactic civilization, sent either to offer new planetary cultures membership in a galactic federation, or eliminate them should they be judged threatening. Magus speculated that our planet was deemed the latter.
His power is in part held by the Apollo Eleven, who could call upon it at will.
Egron the Sifter
The one whom the Astro City populace first saw after he transformed himself from stray matter and started growing a brain stem and nervous system. He seems to be the one who "sifts" through a world through all of the good and bad for observation. After a few days he turned into:
Narmad the Judge
A being that is more of a bluish hue, with some sort of helmet and a sash. He is the presumed judging aspect, whether a planet is worthy of joining either The Continuum. This personality seemed to give Earth a "bad" judgment, but was blinked out by the arrival of the Apollo Eleven who busted seemingly from within.
The manifested form most familiar is...
Kerresh the Devastator
Very dark and destructive, Kerresh is the aspect of the Incarnate that manifests when civilizations that have been deemed unfit and threatening. Its forbidding objective, the complete and total eradication of that civilization. It arose in Astro City in 1982, thanks to Pyramid trying to seize its power by capturing the Apollo Eleven. It was nothing like the passive, entity that formed its tremendous bulk from stray matter five years earlier. Kerresh was now more indiscriminate in acquiring bodily form by absorbing cars, building parts, chunks of ground, and whatever other matter was in the nearby vicinity.
Further, it had the capability for verbal communication. It spoke, and the message it had to deliver was sinister. Despite The Incarnate's seemingly superior power, it was blasted out of existence by the Point Man using the Innocent Gun, which also transformed the Apollo Eleven back into their human form. Earth was saved, but a huge tear in reality started to occur, while the First Family along with Starwoman went to the Continuum to intercede on Earth's behalf. See Rise of Kerresh the Devastator for full detail.
There is also a Shurukk and three others personalities.