Long ago, Atreus was King of Mycenae, the region in Greece where Argos stands at the head of the Gulf of Argolis. His wife Aerope gave birth to two sons, Agamemnon and Menelaus.
Aerope began a love affair with Atreus’ brother Thyestes. Atreus took revenge. He murdered Thyestes’ two sons, diced them up into a stew and served the steaming dish to his brother. After Thyestes had eaten heartily, Atreus revealed the secret of its ingredients, then banished his brother from Mycenae. Later, Thyestes lay with his own daughter Pelopia and fathered a son, Aegisthus. When he came of age, Aegisthus murdered Atreus in vengeance for the old wrongs. Thyestes then reigned in Mycenae. Agamemnon drove him out, in a time before the Trojan War.
For the old wrongs Aegisthus would not find satisfaction until he carried out one further act of revenge on the House of Atreus….
Meanwhile, King Tyndareus of Sparta and his wife Leda had a daughter, Clytemnestra. Clytemnestra married King Tantalus of Pisa (who was either Agamemnon’s uncle or cousin) and bore him a child. In a dispute Agamemnon slew Tantalus and the newborn child, and took Clytemnestra as his own wife. Clytemnestra bore Agamemnon a son, Orestes, and three daughters, Chrysothemis, Electra, and Iphigenia.