Poseidon was a major deity in the Greek pantheon, son of Cronus and Rhea, and brother of Zeus and Hades. He reigned over the sea that was bestowed on him by Fate. As the sea-god he controlled the waves and was liable to attacks of tempestuous waves. In his infancy the Telchines, the magic spirits of Rhodes who specialized in metallurgy and were equally skilful at sculpting images of the gods as well as conjuring up rain and snow, raised him. In adolescence Poseidon married, Halia, the sister of the Telchines who bore him six sons and one daughter, called Rhodus, an eponym of the island of Rhodes.
The god reigned not only over the sea itself, but also the shores; he made rocks and islands tremble and drew forth streams. He is known for his magic trident, an instrument resembling a three-pronged implement of tunny fishers, given to him by the Cyclopes, and his chariot drawn by monstrous creatures, which were half horse and half serpent. Surrounding him was an entourage of sea-creatures including dolphins, nereids, and different spirits of the sea, such as Proteus, the shepherd who watched over Poseidon's seals and could changed himself into any shape that he pleased, or Glaucus, who was mortal-born and earned his living as a fisherman until, by chance, he ate a magic herb, thus becoming a sea-god, joining others like him.
Poseidon sided with Hera against Zeus, for which he was punished by having to enter the service of Laomendon, king of Troy, for whom he built the city walls of Aeneus. But when finishing the work Laomendon refused to pay the agreed sum. The god had his revenge by letting a monster ravage the countryside, which Hercules has to kill after the king was forced to sacrifice his daughter. Poseidon was always hostile to the Trojans and in the war helped the Greeks.
Grimal, Pierre, Larousse World Mythology, Secaucus, New Jersey, Chartwell Books, 1965, pp. 135-136 Cotterell, Arthur, A Dictionary of World Mythology, New York, G. P. Putman's Sons, 1980, p. 154