Riordan

Riordan is a Zombie and former confederate soldier under the service of Ares.

Percy Jackson: Sea of Monsters
When Percy Jackson, Annabeth Chase, and Tyson are swallowed by Charybdis, they encourage Clarisse La Rue and Riordan aboard the CSS Birmingham and the two groups escape the belly of the beast and make their way to Polyphemus' Island.