Leda

In Greek mythology, Leda was a princess who became a Spartan queen. She was married to King Tyndareus of Sparta, and was regarded as one of the era's most beautiful women.

When Zeus saw her, he fell in love with her. He transformed into a swan and appeared in front of her; he seduced her and slept with her. On that night, Leda also lay with her husband. As a result, she became impregnated by both Zeus and Tyndareus. From two eggs, two sets of twins were born; the first set was Helen, the famous Helen of Troy and Clytemnestra; and the other was Castor and Polydeuces. 

The divine swan’s encounter with Leda was a subject depicted by both ancient Greek and Italian Renaissance artists; Leonardo da Vinci undertook a painting of the theme, and Correggio’s Leda is a well-known treatment of the subject. William Butler Yeats’s "Leda and the Swan” is one of the classic poems of literary modernism.