Aegisthus

Aegisthus, in Greek mythology, the son of Thyestes and his daughter Pelopia. Desiring to avenge himself upon his brother Atreus and acting on the advice of the oracle at Delphi, Thyestes consummated an incestuous union with Pelopia. Shortly afterwards, Atreus married Pelopia, not knowing she was his niece. When Aegisthus was born, Atreus accepted him as his own son. Aegisthus later learned his true identity and, urged by Thyestes, killed Atreus. While Agamemnon, king of Mycenae, was away fighting in the Trojan War, Aegisthus became the lover of Queen Clytemnestra. He helped Clytemnestra kill her husband upon his return from Troy. Together with the queen, Aegisthus then ruled Mycenae for seven years; he was murdered by Agamemnon's son Orestes.