Ego was a person, or perhaps an ancient life-form, or perhaps a planet. He could even be called one of the Celestials. Yet no matter what one called him, it never seemed comprehensive enough.
To put it precisely, he was probably a world-ending lunatic who had lived too long and scattered his seed across the universe in hopes of becoming omnipresent. Before he could carry out his grand plan to destroy the universe, Ego needed to find a descendant capable of inheriting his bloodline.
Of course, in Ego's eyes, he was not destroying the universe. He was merely devouring every life-bearing planet in it and turning them into extensions of himself. To be with a god was to attain immortality.
He and Dormammu would probably have had plenty to talk about.
For an old man who had wanted children for many years, being unable to continue his bloodline had been tormenting Ego's heart without end, driving him into a state bordering on madness. He could even personally end the lives of his women—and not swiftly, either, but by making them suffer from illness and pain until they died.
He called it killing his wife to attain the Way, but in truth, it was simply the behavior of a psychological deviant.
And when Taneleer Tivan told Ego about Star-Lord's existence, he became so excited that he suffered a cerebral hemorrhage on the spot. Still, there was no need to panic. It was not a big problem anyway; his human-shaped body was manufactured, so he could simply make another one.
Ego spent a few seconds creating a new body—that of an old father weathered by life, wise, and kindly—then piloted his egg-shaped spaceship toward Sovereign.
Along the way, Ego kept rehearsing what he should say when they met for the first time.