Poseidon is the son of Cronus and Rhea. After his birth, his father swallowed him, and
only his last born brother Zeus saved him and his other siblings, by freeing him.
Then Poseidon held Kronos with his trident at bay while Zeus Kronos and the race of gods, the Titans, with its flashing, finally defeated. When the world was divided into three parts, Zeus received the sky, Hades (another brother of Poseidon) the underworld and Poseidon the sea.
Poseidon was married to Amphitrite, and had with her son Triton, the horse Areion and the daughters and Rhode Benthesikyme.
From numerous love affairs - often with sea nymphs (Nereids, Oceanids) - emerged more children, such as the giant Orion and the one-eyed man-eating Cyclops Polyphemus. The Pegasus, the winged horse, son of Medusa, was also a child of Poseidon.
Poseidon fathered five sets of twins with mortal Kleito of Atlantis. The ten children of this compound were Atlas and Gadeiros (Eumelus in Greek), Ampheres and Euaimon, Mnaseas and Atochthon, Elasippos and Mestor, Azaees and Diaprepes. He told Atlantis on among them and made them kings of Atlantis, where Atlas took over the reign of Poseidon and as the first among them, and King of the main island (this Atlas is not to be confused with the Titan Atlas.)
With the earth goddess Gaia begat Antaeus. At Poseidon's sons is one of the wrestlers Cercyon. He also loved the young Pelops and gave him a magnificent team. Poseidon was the father of the two brothers Otos and Ephialtes, the Aloiden whose mother is Iphimedeia.