In ancient Greece Poseidon was the God of the sea and protector of the waters.  Poseidon was also the God of earth quakes, horses, and storms that occur on the sea. Poseidon was widely worshiped by ancient Greek fishermen. 

Poseidon was the son of the god Cronus and brother of Zeus.  He remained buried within Cronus's stomach until Zeus freed him and his siblings, see Zeus and Cronus, and was one of the twelve  Gods of Olympus.  

Poseidon was said to drive a chariot pulled by horses carrying a trident.  He was attended to by Proteus and old man who could  foretell the future and change form, and the sea goddesses the Nereids.

Poseidon's wife was a sea goddess by the name of Amphitrite who was the granddaughter of the Titan Oceanus.  There was a time when Poseidon wished to marry the goddess Demeter.  Demeter did not want Poseidon and to keep him away she asked the god to make  her a most beautiful animal, a symbol of his love.  Poseidon toiled and toiled and finally he created the first horse.  However, the god Poseidon took so long to create the horse that his love had subsided for Demeter.

Poseidon had a number of children.  His children included the giant Antaeus, Polyphemus the one eyed Cyclops who was blinded by Odysseus in The Odyssey, and Merman who was half human half fish.

Poseidon was greedy and quarrelsome.  This caused problems with the other Gods of Olympus as he was second to Zeus.  A quarrel between him and Athena could be seen in the famous competition of the naming of Athens, see The Naming of Athens.