Antinous, the son of Ares, was tired of being ignored by the gods, that's why he had joined Luke Castellan a few years ago, but now practically the whole camp ignored him barely giving him a second chance. Percy and Annabeth even warned new campers to steer clear of him not only because he had sided with Luke but because of his temper, but that didn't help him feel like any less of an outcast. Eventually, he decided to turn his back on the gods and other demigods like Percy. He got others to join him, creating a small rebellion against the gods.

He honestly somewhat blamed Percy for his life becoming what it is now, and he wasn't a fan of any of Percy's friends seeing them all as lap dogs to the gods.