In ancient Greek religion, god of the sea (and of water generally), earthquakes, and horses. He is distinguished from Pontus, the personification of the sea and the oldest Greek divinity of the waters. The name Poseidon means either “husband of the earth” or “lord of the earth.” Traditionally, he was a son of Cronus (the youngest of the 12 Titans) and of Cronus’s sister and consort Rhea, a fertility goddess. Poseidon was a brother of Zeus.