Pontus
primeval god of the sea.
He was one of the first-born gods and was the father of the most of the ancient sea gods by Gaea.
With his consort Thalassa, they presided over the seas, fish and other sea creatures.
In Greek mythology, Pontus (or Pontos, "sea") was an ancient, pre-Olympian sea-god, son of Gaia and Aether, the Earth and Sky.
Hesiod (Theogony, line 116) says that Gaia brought forth Pontos out of herself, without coupling. For Hesiod, Pontos seems little more than a personification of Sea.
With Gaia, he was the father of the Old Man of the Sea, Nereus and Thaumas (the awe-striking "wonder" of the Sea), of the Sea's dangerous aspects, Phorcys and his sister-consort Ceto, and of the "Strong Goddess" Eurybia.
With Thalassa - whose own name simply means "sea" but in a pre-Greek root - he was the father of the Telchines.
Despite being sidelined, Pontus is still important in Greek mythology because of his family line. With Gaia, Pontus would become father, and subsequently grandfather, to most characters form Greek mythology associated with the sea.
Nereus - The first born son of Pontus and Gaia was Nereus, the god referred to as the Old Man of the Sea. Nereus was associated with the Aegean Sea within the Mediterranean, and was of course father to the Nereids, the water nymphs.
Thaumas – The second son of Pontus and Gaia was Thaumas, a sea god linked with the wonders and dangers of the sea, and with Electra, Thaumas would become father to the likes of the Harpies and Iris.
Phorcys and Ceto – Brother and sister offspring of Pontus would become husband and wife, and as Ceto’s name means “monster” it is not surprising that the pair would become parents to many of the monsters of the deep, including the likes of the Gorgons, the Graeae and the Sirens.
Eurybia – the "strong goddess" was always regarded as a minor sea deity, but was famous in Greek mythology for being the wife of Crius, and subsequently giving birth to Astraeus, Pallas and Perses.
The Fish Pontus was also considered by some writers in antiquity as the father of the fish and other sea life when the sea god partnered with Thalassa, daughter of Aether and Hemera.
Aegaeus – Some writers also named a god called Aegaeus as the son of Pontus and Gaia. Aegaeus was the Greek god of sea storms, and it was after this deity that the Aegean Sea was named.
The Telchines - Pontus was also considered by some to be the father of the four Telchines, minor sea gods associated with the island of Rhodes who were famed for their metalworking skill
Sources
Gaius Julius Hyginus, Fabulae from The Myths of Hyginus
Hesiod, Theogony from The Homeric Hymns and Homerica