Both Castor and Pollux are sons of the mortal woman Leda, but Pollux was the son of Zeus (who famously seduced Leda in the form of a swan), while Castor was the son of Leda's husband, Tyndareus, King of Sparta. Their sisters were Helen, wife of Menelaus (later known as Helen of Troy) and Clytemnestra, wife of Agamemnon.
The twins were worshipped in both Greece and Rome; these are the ruins of the Temple of Castor and Pollux in Rome:
