Janus is a Roman soldier, and member of the Praetorian Guard in Ryse: Son of Rome.
He only appears briefly in Chapter 7, and is immediately slain by Marius. He is indistinguishable from the other Praetorians that are with him.
On his return to Rome, Marius encounters him and a group of other Praetorians assaulting a woman in the amphitheater and orders them to stand down. The Praetorians do not recognize Marius' authority and attack him, and he kills them all in self-defense.
His name is only mentioned after his death when Marius overhears a survivor of the encounter telling his superior that "A legionary murdered Atticus and Janus!".