In the Creation War, Geryon was a front-line, glory seeking soldier of the Nawirrûs Coveant. In one of the war's great battles between leaders, he and four others challenged a very powerful Primordial Lord named Demagihr. This creature had the ability to create spatial rifts, whereby it would step in and out of its surroundings and then reappear somewhere else. Perhaps Demagihr's most dangerous ability was a gas that fused things together. In the melee, two angels fell from grievous wounds. The remaining three were knocked down and stunned as Demagihr appeared above them, popping out of a rift. In a crumpled heap under the beast's mass, they felt their bodies fused together, creating something that look like it crawled out of Chaos. This new form gave the three, bodies joined as one, but minds separate, the power to defeat Demagihr. This new form came at a cost. For decades, mental instability plagued the three as they each tried to assert control over the others. During this time, even though their valor and deeds were great and many, they were shunned. Posted in the rear guarding supply bases and overseeing security forces, Geryon became master of the body and the other two minds.
In the God Era, many of the heroes of the previous war, battled a new enemy. These were the demons hordes of the Abyss; the byproducts of Piranoth's haste to build so many worlds. These abyssal hordes invaded the worlds of the Quara'tun System in what became known as the Demon Spawn War. As in the last century of the Creation War, Geryon found himself again commanding the security forces of Brucrumus operations, that is until he met Asmodeus. When Asmodeus became leader of the Quarat'un Covenant, he promoted Geryon to general and sent him off to Ellubôz. In this system, he carried out a ruthless campaign against the demon hordes invading by way of the river Styx. He also carried out large scale raids on the mortal world Bal-Kriav against the demon prince Yeenoghu and Baphomet. These were mostly done as feints to draw them towards fighting each other or some other demon prince.
When a sentence was passed on Asmodeus, by a council of gods, decreeing that he had defied goodness and embraced acts to further his own might and inflicting undo torment on the enemy, his evil was called out in a number of war crimes, including the sacrifice of troops for what he considered the greater good. Gergyon was caught up in this intrigue, for as Asmodeus's right-hand man, he knew everything and went along with it - such was Asmodeus's charm, and guile. His close association to Asmodeus resulted in him following his master, becoming one of the Fallen Angels. Geryon and the other fallen angels were banished from the Mortal Systems, forced to return to Ellubôz.
When Geryon was cast into what most mortals simply call the Hells, his wings were burned away and his body warped into that of a serpent with three fused torsos. Before the Reckoning, he was the Overlord of Stygia. Even though he never betrayed his master in this reshuffling of Hells' leadership, he was demoted, losing command of his world. It is believed that this was part of a deal to broker peace in the Hells and get back to the business of fighting the demons who were on the brink of seizing Avernus; some say it was the law of the Hells that a world captured goes to the conqueror. For in the Reckoning, Overlord Geryon was out general-ed by Duke Levitus, resulting in him losing control of Stygia. Which ever theory is true, Geryon has remained staunchly loyal to Asmodeus, believing that his old friend has something even bigger in store for him than the title Overlord of Stygia.