Oceanus was the god of water, and one of the Titans, children of Uranus and Gaea. He was thought to have surrounded the whole world with his waters. He was the father of all of the river gods and water nymphs by his wife, Tethys. The following were some of his children: Asopus, Doris, Nemesis, Inachus, Perse, Achelous, and Metis.
In early times, the earth was thought of as being a flat disk surrounded by a perpetual river - this river was Oceanus. Later, as knowledge advanced, Oceanus was said to be the outer seas that surrounded the lands, in particular the Atlantic. The Atlantic, named after Atlas, was often called simply Oceanus.