The Nereus reference article from the English Wikipedia on 24-Apr-2004
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Nereus

Nereus: in Greek Mythology, eldest son of Pontus and Gaia. See Hesiod, Theogony 233-36.

A Titan who, with Doris, fathered the Nereids. Together, he lived with his family in the Aegean Sea. He was a shapeshifter with the power of prophesy and he would aid heroes, such as Heracles, who managed to catch him even as he changed shapes.

Nereus was the god of the sea prior to being supplanted by Poseidon when the latter's brother Zeus overthrew Cronus.