This Eternal, like every other, was created by the Celestials one million years ago. Around 3000 BC, he became Gilgamesh, king of Uruk in Sumeria. (modern-day Iraq).
In ancient times, the mighty Eternal roamed the Earth aiding ordinary human beings by overthrowing tyrants and slaying dangerous beasts. Somehow unaware of his membership to the Eternals, he quested for eternal life. He was often mistaken for (and consequently known as) Samson and Hercules.
In 1271 BC, he cleaned the Augean Stables for Hercules on his behalf (but unknown to Hercules) by diverting two rivers through the Stables.
Apparently, like Hercules, he took Atlas's burden on his shoulders.
At undisclosed times, he and Hercules fought side by side on the walls at Ertatha and bested the Demon-Dragon Zu.
At some point, he befriended Achilles. He befriended Aeneas and helped him conquer the Latium, laying the foundations of the Roman Empire. He also befriended King David. He fought for the Roman Empire as a Centurion, slaying many tribes in their name.
During the 19th century, he aided in the translation of the Rosetta Stone. He also joined Buffalo Bill's Wild West Show picking up a few tricks along the way.
Eventually, he learned of his true heritage, and Zuras, leader of the Eternals, confined the Forgotten One to a sector of the Eternal city of Olympia. It is said that Zuras' reason for this action was the Forgotten One's pride and his insistence on intervening in human affairs. As yet, no details of these charges have been revealed. The Forgotten One remained banished to this sector, which the other Eternals shunned, for centuries.
While virtually all of the Eternals were meeting in the form of the Uni-Mind, the Deviants (natural enemies of the Eternals) launched a spacecraft containing a powerful energy bomb, in the hope of destroying the mother ship of the Fourth Host of the Celestials. Sprite, an Eternal left behind to monitor Earth, learned of the Deviants' plan and feared that the Celestials would retaliate by wreaking havoc on Earth. Sprite sought out the Forgotten One and equipped him with an armored costume and a spaceship. The Forgotten One traveled into space, and the Fourth Host's leader, the One Above All, teleported him into the Deviants' spacecraft. The Forgotten One wrecked the energy bomb and its spacecraft just before the moment of detonation. Then, floating stunned in space, the Forgotten One was drawn into the mother ship of the Fourth Host.
Sometime later, the Forgotten One reappeared on Earth and was temporarily blind (the cause of this blindness remains a mystery since Eternals cannot be injured by conventional means). Possibly the power released by the energy bomb as he wrecked it was sufficient to blind him. He delivered what he said was a message from the Celestials to the Eternals, which was to not interfere with the Celestials' plans.
In recognition of the Forgotten One's bravery, Zuras restored his freedom to him and renamed him Hero, a name that the Forgotten One has abandoned.
But the mission that the Celestials gave the Forgotten One went far beyond delivering that simple message. Exactly what that mission remains unrevealed. However, to carry that mission out, the Forgotten One went to the city of the Deviants in undersea Lemuria some months later. Disguised in a hood and robes, the Forgotten One accompanied Kro, the new ruler of the Deviants, on his mission to the Pyramid of the Winds. Also, in the interim, the Forgotten One regained his sight.
Later, the Forgotten One traveled to New York, during a time of demon invasion. He joined other heroes in saving the son of Mr. Fantastic and the Invisible Woman and remained with them to reform the hero team Avengers, whose ranks were depleted. He readopted the name Gilgamesh, at the prompting of Mr. Fantastic. After several adventures with the Avengers, he sustained grave injuries in the battle versus the Lava Men and the extradimensional Blastaar. He was returned by the Avengers to Olympia to recuperate.
Gilgamesh was later kidnapped by the Avengers' archenemy Immortus, posing as the time-traveling villain Kang. As part of Immortus' ruse as Kang, he allowed Gilgamesh to be killed by his underling Neut.
Seemingly killed, Gilgamesh was reborn in a new body. Soon after, fellow Eternal, Sprite, angered after millennia stuck in the form of a child, tapped into the power of the Dreaming Celestial to make all Eternals forget their heritage and placed them into human guises. After Sprite's death, separate factions of Eternals worked to find and reawaken the lost Eternals. Ajak, working on his own, discovered the Forgotten One in Brazil, working as a circus strongman named O Guerreiro, or "The Warrior." Ajak then "reminded" the Forgotten One of the other Eternals, showing him warped images of them, and reawakening him to his true power. He attacked fellow Eternal Druig and told him to warn the others that he was coming for them as revenge for their perceived betrayal that Ajak had shown him. He then arrived at Olympia in Antarctica and attacked Makkari. He went so far as to destroy Makkari's reforming body and the whole Activation Chamber. He was eventually stopped by Thena and seemingly regained his true memories before she slew him.
Claiming to have been endowed with a gift of awareness by the Dreaming Celestial and the idea that he was part of a greater pattern, he went to Lemuria as the Forgotten One (while no longer using the name of Gilgamesh). There he met Thor who had come to liberate Phastos, kidnapped along with the Activation Chamber by the Deviants who needed them to save their dying species.
Guiding Thor to attack the Deviant Throne Room where Ghaur was torturing his allies, he left Thor to battle, stating he was needed elsewhere and that Thor would barely recall meeting him.
When Thanos was unexpectedly resurrected and began killing Eternals as well as sabotaging the machine of resurrection, a traitor was suspected among the Eternals. The Eternals narrowed their field of suspects down to Gilgamesh. To confront him, Sersi pretended to attack Tony Stark to lure Gilgamesh out of his extradimensional home. After Gilgamesh was restrained and interrogated, he forced his accusers to let him prove his innocence with gunmen that worked for him. They went to the Exclusion where the machines of the resurrection were located and Gilgamesh showed how he would sabotage the machines but also revealed that Phastos knew this as well, revealing that Phastos was the traitor. As Gilgamesh and the Eternals went to confront Phastos, Thanos was preparing to ambush them.
Gilgamesh and his fellow Eternals were able to overwhelm Thanos, but then Phastos accidentally teleported him and the others all over Earth while trying to teleport them to the Exclusion to help him fix the resurrection machine he broke. Ikaris gave his life to use his matter manipulation power to repair the machine. Gilgamesh and the others later learned the reason for Phastos' actions: Eternals were resurrected at the cost of human lives and resurrection machines couldn't be turned off without endangering Earth. Gilgamesh was devastated after learning this as every time he killed an Eternal as punishment and they were resurrected, human lives were taken.
