Castor and Pollux were twin brothers in Greek and Roman mythology. Together they are called the Dioscuri. They were the sons of Queen Leda of Sparta. Their twin sisters were Helen of Troy and Clytemnestra. Castor and Pollux were changed into the constellation called Gemini. Tyndareus, the king of Sparta, was the father of Castor, which made Castor mortal, while Zeus was the father of Pollux which made him a demigod.