Nereus

n. ancient Greek sea god, son of Gaia and Pontus, father of the Nereids (Greek Mythology)

Nereus, in Greek Mythology, was the eldest son of Pontus and Gaia, the Sea and the Earth, a Titan who (with Doris) fathered the Nereids, with whom Nereus lived in the Aegean Sea. In the Iliad the Old Man of the Sea (άλίός γέρών) is the father of Nereids, though Nereus is not directly named. He was one of the manifestations of the Old Man of the Sea, never more so than when he was described, like Proteus, as a shapeshifter with the power of prophecy, who would aid heroes such as Heracles who managed to catch him even as he changed shapes. Nereus and Proteus ("first") seem to be two manifestations of the god of the sea who was supplanted by Poseidon when Zeus overthrew Cronus.
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Noun
1. (Greek mythology) a sea god son of Pontus and Gaea; lived in the depths of the sea with his wife Doris and their daughters the Nereids
(hypernym) Greek deity
(classification) Greek mythology

[Greek] Nereus is the righteous and all-wise "old man of the sea", god of the Mediterranean Sea, son of Gaia and Pontus. His wife is Doris and she became by him the mother of the fifty Nereids, friendly sea-nymps. Nereus is a gentle and very wise old man who has the power to foretell the future, but he will not answer questions unless he was caught and to avoid that he would change his shape (such as when Heracles came to ask him the way to the Garden of the Hesperides). The domain of Nereus and his fifty daughters is especially he Aegean Sea where he has saved many ships from destruction.

Nereus, Nereids Nereus pertains to the enclosed seas near Greece, in contradistinction to the ocean and the fresh waters. He is a later variant of Poseidon, the former ruling the sea in Atlantean times, the latter taking his place with the fifth root-race. The Nereids, the fifty daughters of Nereus, belong to the class of nature spirits presiding over water and recognized by various propitiatory rites. Like water spirits in general, they were beautiful maidens. Goats were sacrificed to them -- a sign of their connection with the mysterious sign Capricorn.
Nature spirits include elementals both slightly developed and relatively highly developed, existing in widely diverse classes. There are elementals of high spiritual character possessing intellectual attributes and extensive sway over the kingdoms of nature; whereas others are but tiny elemental entities with relatively insignificant power.