NEREUS ~ THE ELDER GOD OF THE SEA

Nereus,  (Ancient Greek: Νηρεύς) is the eldest son of Pontus (the Sea) and Gaia (the Earth). He and Doris are the parents of the Nereids and Nerites, with whom Nereus lives in the Aegean.
In Ancient Greece , He is described the 'Old Man of the Sea'. In Aelian's natural history, written in the early 3rd century CE,Nereus is mentioned as the father of a watery consort of Aphrodite, named Nerites, who was transformed into "a shellfish with a spiral shell, small in size but of unsurpassing beauty." Another well-known daughter of Nereus is Thetis, the Nereid mother of the Greek Hero Achilles. Amphitrite, the consort of Poseidon is also one of His children.

Like Proteus, Nereus can shapeshift and is a powerful oracle. He helped heroes such as Heracles, who managed to overpowerhim as He transformed constantly. 

During the course of the 5th century BCE, Nereus was gradually replaced by Triton, who does not appear in Homer, in the imagery of the struggle between Heracles and the sea-God who had to be restrained in order to deliver his information that was employed by the vase-painters, independent of any literary testimony.

In a late appearance, according to a fragmentary papyrus, Alexander the Great paused at the Syrian seashore before the climacteric battle of Issus (333 BCE), and prayed, "calling on Thetis, Nereus and the Nereids, Nymphs of the sea, and invoking Poseidon the Sea-God, for whom he ordered a four-horse chariot to be cast into the waves."

Nereus is a benevolent Sea-God, known for His kind nature and the respect He shows for Divine Order. He is also known for his truthfulness and virtue.

The Attic vase-painters showed the draped torso of Nereus issuing from a long coiling scaly fishlike tail. Bearded Nereus generally wields a staff of authority. He was also shown in scenes depicting the flight of the Nereides, as Peleus wrestled their sister Thetis.

In general, Nereus and His family represent everything beautiful and positive within the marine environment; the aspect of the sea which provides mortals with nourishment and favourable conditions for expeditions and commerce.

Edited from : Wikipedia