The Spartan soldier, Aeon Calcos, like Sophitia, was one of the twenty-four warriors to receive an oracle from the god Hephaestus to destroy Soul Edge–one for every letter of the Greek alphabet. Armed with the holy Xi Sword forged for him, a group of desert travelers rescued a dehydrated Aeon and brought him to their village, and he was about to repay them by teaching them swordplay. He was unable to exchange their kindness, however, as the Evil Seed had rained down and turned Aeon into a crazed killer, causing him to massacre everyone in the village.
Kunpaetku, the grand priest of the cult order Fygul Cestemus, eventually heard stories of him and captured Aeon so that he may be used as a human guinea pig in a terrible experiment, causing him to transform into a lizardman — the first of many lizardmen to come. Aeon was ordered to bring Rock's adopted son, Bangoo, to Europe so that his soul could be stolen. Aeon was eventually tracked down and defeated by Rock for the kidnapping, while aiding Astaroth in pursuing Soul Edge.
Soul Edge was struck down moments later, the energy emitted from Soul Calibur releasing Aeon from his brainwashed state. Hidden from the world, Lizardman set on a journey to restore his human form, however upon realising he had no place to return to, he wondered angrily why Hephaestus had not helped him in his time of need. "My god has forsaken me," he thought, before casting away the sword and shield he was given, to find Soul Edge and destroy the god of forgery with the very weapon he feared most would be his new resolve and the ultimate revenge.
In Soul Calibur IV, Lizardman had been, slowly, but gradually, losing his human feelings and memories, until finally, even his own heart had become one that belonged to a monster. Before he knew it, other Lizardmen surrounded him, but he successfully defeated all of them. Soon, he became their leader, leading them on violent rampages.
But at night, he would have memories of being human. He didn't even know what he was. All he felt was emptiness. Suddenly, he realized that he was missing his soul. As he wondered of what has become of it, another memory struck him. His soul was inside Soul Edge. He now searches for the evil sword to obtain his lost soul.