Kallistos was previously a soldier in Ptolemy XIII's army. As he had trouble obeying orders and had to support his family, Kallistos left the army and pursued a career in the gladiator arena in Krokodilopolis. In 48 BCE in the arena, Kallistos met the Medjay Bayek of Siwa, who had newly joined the competition and teamed up with his fellow Siwan and childhood friend, Kensa. When Bayek asked if he had challenged the Gallic Brothers, Viridovix and Diovicos, Kallistos remarked that he wasn't worthy and considered himself to be fortunate.
After the Medjay had won his first round in the arena, Kallistos congratulated Bayek on his win. As Bayek asked him about mercenary contracts, Kallistos gave him some advice, encouraging him to take up the offers as they come. Eventually, Kallistos proved himself worthy to be offered a contract, which he accepted, despite warnings from Horus, a retired gladiator. However, Kallistos did not succeed in his mission, which resulted in his death. His body was later brought back to the arena, where he was attended to by Horus.
- Kallistos, Καλλιστος, is a Greek name meaning 'most beautiful'.