Leda.
    Wife of Tyndareus, king of Sparta, Leda was the mother of the Dioscuri (Castor and Polydeuces), Clytemnestra, and Helen of Troy. Zeus (Jupiter) desired her and, approaching her in the guise of a beautiful swan, impregnated her. Sources differ over which children Leda bore as a result of her union with the god: Helen and Polydeuces (Pollux) are usually considered Zeus’s offspring; Castor and Clytemnestra are called the children of Tyndareus. However, some accounts cite both of the Dioscuri as Zeus’s sons. In some versions, the children of Zeus were born from an egg that Leda laid after her intercourse with the swan. A variant of this version states that the egg was the product of a union between Zeus as a swan and Nemesis, and was given to Leda to nurture; only Helen was born from it and was raised as Leda’s own daughter.


Further Reference: Clive Scott (1979), "A Theme and a Form: Leda and the Swan and the Sonnet," Modern Language Review 74:1-11 DOI: 10.2307/3726899