Poseidon was the Greek god of sea and water. He was later known as Neptune.
Poseidon was one of the three sons of Cronus, he and his brothers, Zeus and Pluto killed their father and divided the world among them--Poseidon getting the fluid part. He lived in a golden palace beneath the waves, where he caused both storms and favoring winds. Sailors, naturally, worshiped him, and he was thought of as the god of navigation. His trident was used to lash the sea to fury, cause springs to gush from the ground, and cause earthquakes. For this last reason, one of his descriptive names was enosichthon, which translates like "a real earth shaker!". The Romans gave him the name Neptune.