Sometime during the Peloponnesian War, Zetes was part of a group of mercenaries, hired by the Cult of Kosmos, who ventured into the Petrified Temple within the Petrified Valley in order to recover an artifact therein.
The mercenaries initially planned to break into the temple and corner the Writhing Dread but it ambushed them before they gained entry. Incapable of forming a strategy, they focused on surviving. A woman delivered the killing blow on the creature, making it drop the artifact. Zetes tried to stop her from touching it but the curse gripped her as she became the next Writhing Dread. Fortunately for him, he was able to escape by using his trusty spear to keep the monster away.
At the height of the war, the Spartan misthios Kassandra confronted Zetes at the temple of Poseidon in Lesbos. Sent by Bryce, Ligeia's lover, Kassandra asked Zetes about the monster. Changed by his experience of seeing "true evil", he recounted his story to Kassandra. After telling her that his spear was what had saved him, she demanded he hand it over. Zetes refused, and they fought, with Kassandra defeating Zetes and taking the spear for herself.
Equipment and skills
Zetes' signature spear, the aptly named Gorgon Slayer, was the sole reason he survived his encounter with the Writhing Dread. Changed by that experience, Zetes retired, though he was still sought out by other mercenaries for his wisdom. He had sufficient skill with the spear, being able to hold off the Writhing Dread, but he could not hold up to the likes of Kassandra, and as a warrior, refused to give up his spear without a fight.
Behind the scenes
Zetes, a character in Assassin's Creed: Odyssey, shares his name with the mythological figure, one of the two sons of Boreas, the Greek god of the north wind. The Boreads Zetes and Calais served as Argonauts, and were pivotal in driving away the harpies that terrorized Phineus of Salmydessus. The brothers were subsequently killed by Herakles out of vengeance for convincing the rest of the Argonauts to leave him behind while he searched for his companion Hylas.
While Zetes can be defeated, he can also be knocked out and recruited as a lieutenant for the Adrestia.