Aigisthos

In Greek mythology, Aegisthus (Gr. , "goat strength" — also  transliterated as Aegisthos or Aigísthos) was the son of Thyestes and of his daughter, Pelopia.Thyestes felt he had been deprived of the Mycenean throne unfairly by his brother, Atreus. The two battled back and forth several times. In addition, Thyestes had an affair with Atreus' wife, Aerope. In revenge, Atreus killed Thyestes' sons and served them to him unknowingly. After eating his own sons' corpses, Thyestes asked an oracle how best to gain revenge. The advice was to father a son with his own daughter, Pelopia, and that son would kill Atreus.
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[Greek heroic] The son of Thyestes and his daughter Pelopea. Desiring to avenge himself upon his brother Atreus and acting on the advice of the oracle at Delphi, Thyestes consummated an incestuous union with his daughter Pelopia. Shortly afterward, Atreus married Pelopia, not knowing she was his niece. When Aegisthus was born, Atreus accepted him as his own son, not knowing that he had been fathered by Thyestes. 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 later murdered by Agamemnon's son Orestes.