Oceanus,
in Greek mythology, one of the Titans, the son of Uranus and Gaea. With his wife, the Titan Tethys, he ruled over Ocean, a great river encircling the earth, which was believed to be a flat circle. The nymphs of this great river, the Oceanids, were their daughters, and the gods of all the streams on earth were their sons. In later legends, when Zeus, chief of the Olympian gods, and his brothers, Poseidon and Hades, overthrew the Titans and assumed their power, Poseidon and his wife, Amphitrite, succeeded Oceanus and Tethys as rulers of the waters.