(Spoiler alert! - sort of
Stern is one of the support units from project exodus. Taken back to the Roman era (Caligula's reign) he is hacked by Rashim to take Caligula's orders. However, Caligula betrays the time travellers, and slaughters all but Rashim; whom is muzzled and locked up. The ordinary Romans fear him and his colleagues - including Chuck and Butch - knowing of their superhuman strength. They name them 'Stone Men'. This prevents attempts to assassinate Caligula, who everyone hates.