Out of all the playable characters in the series, Aeon has had his weapon style changed from: sword & shield, axe & shield and then dual axes.
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 & Game Shield forged for him, he set off on his journey. However, he became lost in a vast desert and eventually collapsed. A group of kindly 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 rained down and temporarily changed Aeon into a mindless killer, causing him to slaughter everyone in the village.
Kunpaetku, the grand priest of the cult order Fygul Cestemus, eventually heard stories of him and captured Calcos so that he may be used as a human guinea pig in a diabolical experiment, causing him to transform into a lizard —the first of many lizardmen to come. Calcos was ordered to bring Rock's adopted son, Bangoo, so that his soul could be stolen. The creature 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 Lizardman from his brainwashed state —although he remained in his transformed body. At first, he was not certain about his true self, but his sacred weapons reassured him, that he was once human. Initially, he wished to return to his home and family, but he realized that they will not recognize him in that state. Hidden from the world, Lizardman set out on a journey to restore his human form, but with time passing with no signs of cure, he fell into despair. As a last resort, he visited the temple where he was transformed in hope of finding a cure, but found only ruins. With his last glimmer of hope gone, 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, and, bearing a new shield and a war axe, decided to find Soul Edge and destroy the god of forgery with the very weapon he feared most. This would be his new resolve and the ultimate revenge.
He possibly has a family in his homeland (according to the information in Soulcalibur III), but they are no longer important to him.
Overtime, Lizardman slowly, but gradually, lost 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, and with his superior strength and battle technique he dominated the group. Soon, he became their leader, leading them on violent rampages.
But at night, he would have dreams revisiting the feelings and memories of being human. He didn't even know what he was anymore. 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.
"Why? he pleaded. "Why has my god forsaken me in my time of need?!"
In despair at the loss of his humanity, Aeon eventually surrendered to his beastly instincts: He walked on all fours and devoured anyone —or anything— that crossed his path.
Many years passed, until one day Aeon heard an inhuman voice speaking to him inside a cave.
"Devour all, and your wish shall surely come true."
From that moment on, the beast-man gained the power to inherit the nature of those he consumed. Each time he tasted the blood of new prey, his body and soul were transformed.
Gradually he regained the power of reason. Aeon searched the faint remnants of his memory...
"How can I regain that which I have lost?" he wondered.
But he knew the answer: He must feed on new victims. He must consume the flesh of holy warriors...