Poseidon was one of the twelve Olympian gods in ancient Greek religion and mythology. He was the god of the sea, storms, earthquakes, and horses. His Roman equivalent is Neptune.
Poseidon was the son of Cronus and Rhea, making him a grandson of Uranus and Gaia. He had three brothers: Zeus, Hades, and Demeter; and three sisters: Hestia, Hera, and Aphrodite. He married Amphitrite, an oceanid nymph. By her he had two sons: Triton and Rhode; by Aethra he fathered Theseus; by Amymone he became the father of Nauplius; by Beroe he sired Nausithous; by Celaeno he begot Lycus & Eurypylus; by Charybdis he engendered Scylla & Cromys; while on Cerceis (a daughter of Oceanus) Poseidon begat Circe & Aeetes (who ruled over Colchis). Other children of Poseidon were Polyphemus (by Thoosa), Glaucus (by Leucippe), Orneus (by Alcyone), Bellerophon (by Anteia/Sthenoboea), Melicertes or Palaemon (wrestler), Lagon etc.
In most accounts abducting Persephone to be his wife poseidon produced three children together including Arion with Hippodamia having given birth to one child before being abducted herself despoina also called Kore who would grow up to become persephones replacement as queen of the underworld after she was abducted herself another name for Kore is Cora which means maiden signifying her virginity another child from this union was Zagreus whose story is a bit more tragic Zagreuz was killed as an infant by Titans who dismembered him cooking some parts boiling others baking some roasting them finally eating him however Zeus rescued what remained heart mind soul etc reconstructing zagreuz into Dionysos so that not all hope would be forever lost for humanity but that we could partake in divine ecstasy as well
Another figure sometimes associated with Poseidon's family is Melisseus who may have either been a son or brother Melisseus along with his wife Iole parented six daughters known collectively as The Oenotropae meaning wine-growers these were women cursed to bring forth nothing