Poseidon was the Ancient Greek god of water, the sea, horses, storms, and of earthquakes. He was the second most important god in the Greek pantheon. His Roman equivalent was Neptune. Sailors developed the Line-crossing Ceremony in tribute to him, which in some seafaring services survives in a humorous fashion.
Poseidon outlasted the displacement of the Ancient Greek pantheon by Christianity as Greece's dominant religion. In modern times, he was rejuvenated by insincere gestures of worship and contributions to his temple funds by assorted government organizations who thought he might be useful. One such was the Barony of Angels, which contracted with the sea god to provide water for its sewer system. There was concern that, despite his desperation to have as many worshipers as possible, however insincere, Poseidon would be too proud to agree to something so menial.