Leda was the daughter of Thestius, and eventually was married to Tyndareus, king of Sparta. She was seduced by Zeus when he came to her disguised as a swan. He made love to her, and later that night she also made love to her husband Tyndareus. The result was the birth of four children (generally said to come from two eggs). The children included boys Castor and Polydeuces, called the Dioscuri, and girls Clytaemnestra and Helen. Helen and Polydeuces were the children of Zeus, and immortal, but Castor and Clytaemnestra, were Tyndareus' children, and mortal.
Leda is said to have died due to the shame related to the deeds committed by Helen (of Troy).