Oceanus and Tethys were the Titans of the sea and were children of Gaea the Earth and Uranus the Heavens. Although they and their fellow Titans of Myth enjoyed god-like status, Gaea had other offspring who were ugly and monstrous. Uranus banished them to the pits of Tartarus.
Gaea persuaded Cronus to kill Uranus and free the brood. Cronus completed the first part of the pact only and then invited Oceanus and the other Titans of Myth to join him in the paradise of a subjugated Earth.
Many years later, Cronus' son Zeus released the brood from Tartarus and overthrew the Titans of Myth. Oceanus and the others were trapped in pillars of stone in Tartarus. After Thousands of years, Thia and Hyperion managed to free themselves, and with the help of Donna (Wonder Girl) Troy, they released Oceanus and the others. Oceanus then joined the rest of the Titans of Myth as they attacked Mount Olympus.
Two epic battles followed, in the final one, Oceanus' wife Tethys was among those killed by an insane Thia, and as the hostilities ended, Zeus inited the surviving Titans of Myth to join him inside Olympus to live in peace. Oceanus and the others accepted.