The brothers Zeus (Jupiter), Poseidon (Neptune) and Hades (Pluto), deposed their father Cronus for control of the world.
After this task was completed, they puts lots in a helmet to learn who would control the sky, sea and underworld, leaving
the earth as common ground to all. Zeus drew the lot for the sky, Poseidon became ruler of the seas and Hades became
master of the underworld.
Poseidon needed a wife who could be comfortable in the depths of the sea and commenced searching everywhere to find a suitable mate. He found and courted Thetis the Nereid (sea-nymph). But when Poseidon learned it was prophesied that any son born to Thetis would be greater than his father, he backed off, allowing her to marry a mortal named Peleus and Poseidon continued his quest.
He next approached Amphitrite, who he had seen dancing on the island of Naxos and fell in love with. Upon learning of his intentions, Amphitrite fled to the Atlas Mountains for protection and escape.Poseidon sent his sea-creatures as messengers searching after her. Among these was Delphinus, who once he located her, pleaded Poseidon’s case so convincingly to Amphitrite, she yielded and consented to the marriage. For this act, Poseidon set Delphinus’s image among the stars as a constellation – Delphinus the Dolphin.