Clytemnestra was the daughter of Tyndareus and Leda, the king and queen of Sparta. According to the myth, Zeus appeared to Leda in the form of a swan, seducing and impregnating her. Leda produced four offspring from two eggs: Castor and Clytemnestra from one egg, and Helen and Polydeuces from the other. Therefore, Castor and Clytemnestra were fathered by Tyndareus, whereas Helen and Polydeuces were fathered by Zeus.
Agamemnon and his brother Menelaus were in exile at the home of Tyndareus. In due time the brothers married Tyndareus’ two daughters: Agamemnon marrying Clytemnestra and Menelaus marrying Helen. In a late variation, Euripides’s Iphigenia at Aulis, Clytemnestra’s first husband was Tantalus, King of Pisa (in the western Peloponnese), who was slain by Agamemnon. Agamemnon also murdered his infant son. He then forcibly made Clytemnestra his wife. In another version, her first husband was King of Lydia, which was known to the Greeks for its shrine of the labrys, the double-bladed ax that some say Clytemnestra used to kill Agamemnon:
After Helen went (or was taken) from Sparta to Troy, her husband, Menelaus, asked his brother Agamemnon for help. Greek forces gathered at Aulis. However, consistently weak winds prevented the fleet from sailing. Through a subplot involving the gods and omens, the priest Calchas said the winds would be favorable if Agamemnon sacrificed his daughter Iphigenia to the goddess Artemis. Agamemnon persuaded Clytemnestra to send Iphigenia by deceptively telling her that the purpose of his daughter’s visit was to marry her to Achilles. When Iphigenia arrived at Aulis, she was sacrificed, the winds turned, and the troops set sail for Troy. Clytemnestra learned of this event and grieved for her daughter.
The Trojan War lasted ten years. During this period of Agamemnon’s long absence, Clytemnestra began a love affair with Aegisthus, her husband’s cousin. Whether Clytemnestra was seduced into the affair or entered into it independently differs according to the respective author of the myth. Nevertheless, Clytemnestra, enraged by Iphigenia’s murder (and presumably the earlier murder of her first husband by Agamemnon, and her subsequent rape and forced marriage), and Aegisthus, whose father Thyestes was horribly betrayed by Agamemnon’s father Atreus, and who was conceived specifically to take revenge on that branch of the family, began plotting Agamemnon’s demise.
Clytemnestra has been the subject of many artistic works.