Janus of the Roman Gods

In ancient Roman religion and myth, Janus (/ˈdʒeɪnəs/ JAY-nəs; Latin: IANVS (Iānus),  pronounced  [ˈjaːnʊs]) is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. From Wikipedia.

During the Second Olympian War, he joined the Titans, like many other of his fellow minor gods. From Riordan Wiki.