In Greek mythology, Leda (ˈliːdə,_ˈleɪ-; Ancient Greek: Λήδα lɛɛ́daː) was an Aetolian princess who became a Spartan queen. According to Ovid, she was famed for her beautiful black hair and snowy skin. Her myth gave rise to the popular motif in Renaissance and later art of Leda and the Swan.
Leda was the daughter of the Aetolian King Thestius hence she was also called Thestias. Her mother was either Leucippe, Deidameia, daughter of Perieres, Eurythemis, daughter of Cleoboea, or Laophonte, daughter of Pleuron. According to Alcman, Leda's parents were Glaucus and Laophonte while Eumelus attested that they are Sisyphus and Panteiduia or Paneidyia.
She married king Tyndareus of Sparta and by him became the mother of Helen of Troy, Clytemnestra, Castor, and Pollux (also called "Polydeuces"). Leda also had three other daughters by Tyndareus: Timandra, Phoebe, and Philonoe.
Leda was admired by Zeus, who seduced her in the guise of a swan. As a swan, Zeus fell into her arms for protection from a pursuing eagle. Their consummation, on the same night as Leda lay with her husband Tyndareus, resulted in two eggs from which hatched Helen (later known as the beautiful "Helen of Troy"), Clytemnestra, and Castor and Pollux (also known as the Dioscuri). Which children are the progeny of Tyndareus the mortal king, and which are of Zeus and thus half-immortal, is not consistent among accounts, nor is which child hatched from which egg. The split is almost always half mortal, half divine, although the pairings do not always reflect the children's heritage pairings. Castor and Pollux are sometimes both mortal, sometimes both divine. One consistent point is that if only one of them is immortal, it is Pollux. It is also always stated that Helen is the daughter of Zeus.
In Homer's Iliad, Helen looks down from the walls of Troy and wonders why she does not see her brothers among the Achaeans. The narrator remarks that they are both already dead and buried back in their homeland of Lacedaemon, thus suggesting that at least in the Homeric tradition, both were mortal.