Origin

Much like other planets, Ego formed from gas and dust. Ulike the other planents, Ego was able to to move of his own volition and he could talk. In order to continue living, Ego must eat space crafts and other planets. Ego's absorbtion of planets did not go unoticed, the Rigellians feared their planent would get absorbed by Ego. In order to save their planet, they made a deal with Thor. If Thor prevented the Rigellians planet from absorbtion, then the Rigellians would leave Earth alone. After an epic battle, Thor won and Ego promised that he would never leave the Black Galaxy. Later, Galactus found his way into Ego's space and wanted to eat Ego. Thor came to Ego's aid and the two stopped Galactus. Ego was now in Thor's debt so he allowed a group called the Wanderers live on him. A Rigellian took a sample of Ego, so he could use it to fertilize sterile worlds being considered for habitation. This drove Ego insane and caused him to start absorbing the Wanderers. Thor, with the aid of Galactus, Galactus' herald Firelord, and Hercules, stopped Ego by attaching an engine to Ego's south pole. This engine made Ego fly through space uncontrollably, rendering Ego harmless to other planets.

Ego's Attacks on Earth

Ego eventually learned how to control the mechanism and he searched the galaxy for Galactus in hopes of revenge. He eventually tracked Galactus to Earth, but there was no signs of Galactus, so he attacked Earth. The Fantastic Fourand a mutant known as L.R "Skip" Collins defended Earth from Ego's attack. Ego was destroyed when Thing took Ego's engine and threw it into Ego's brain, causing him to fly into the sun.

Ego did not stay destroyed for long, he eventually reformed and joined the Elders of the Universe. The Elders planned to destroy Galactus, but Ego was sidelined before the confrontation when defeated by the Silver Surfer. After Ego was used as a pawn by Supreme Intelligence, he threatened Earth for the last time. He was stopped when he was absorbed into Quasar's Quantum Bands.

At some point he was presumably freed since then.

Alternate Realities

Earth-2149: Also known as Marvel Zombies, in this universe, the Marvel Zombies chewed apon Ego.

Earth-9602: In this universe, where Marvel and DC were combined, Ego was combined with Oa to make Oa the Living Planet.