"Pontus sired truthful Nereus, his oldest son,
who tells no lies; they call him the old man
because he is honest and gentle and never forgetful
of right, but ever mindful of just and genial thought."
From this description, it is easy understand why the ancient Greeks regarded Nereus as a wise and just Old Man of the Sea. Indeed, some sources state that Nereus had the gift of prophecy. This gift, however useful, also occasionally brought conflict. One case in point involves the hero Herakles, who, according to one version of the story, had to catch Nereus and make the sea god tell him the location of the Garden of the Hesperides.
The sea god is also credited with fathering fifty beautiful daughters with his wife, the Oceanid Doris. These sea nymphs are collectively known as the Nereids, a name derived from that of their father. Some of these sea goddesses played significant roles in myth. A few noteworthy Nereids are Amphitrite, Galatea, Psamathe, and Thetis.
In addition it is worth noting that Nereus and his daughters the Nereids were thought to dwell together in the sea. Indeed, there is a scene in Homer's Iliad in which Thetis is invoked by her son Achilles. Homer describes how the sea nymph emerges from her home in the following manner: "...her ladyship [Thetis] his mother heard him in green deeps where she lolled near her old father. Gliding she rose and broke like mist from the inshore grey sea face, to sit down softly before him..." (Iliad, Book I, 358 ff.).
Who's Who in Classical Mythology