Janus

Janus is the minor Roman god of choices, doorways, beginnings, and endings.

Janus apparently seemed to have sided with the Titans during the last Olympian War, in actuality he had been working with Zagreus since the Age of Myth as one of his Lieutenants, his true Human form having been unseen outside of the Ark since the mythical age.

Trivia

 * Janus has no Greek form, but he does have a Greek name: "Ιανός (Ianós)".