This lovely lady was the queen of Sparta and the mother of Castor and Pollux, who were said to have hatched from a big old egg that she laid. Why would a human queen lay an egg, you ask? Because she mated with Zeus while he was in the form of a swan, of course. Later that night, she also slept with her husband King Tyndareus, which is why both of the Dioscuri weren't immortal. Go-figure stories like this pop up all the time in Greek mythology. Leda is one of many mothers of demi-god heroes who was said to have mated with her husband and a god in the same night, therefore giving their son half-god status. Another great example is Aethra, mother of Theseus.