In Greek mythology, Pelopia, Pelopea, or Pelopeia (Ancient Greek: Πελόπεια) — less commonly Mnesiphane — was the daughter of Thyestes and the mother of Aegisthus. An oracle told Thyestes that a son by his own daughter would kill Atreus; the resulting incestuous conception, recognition by a sword, and Pelopia's suicide form a central episode of the Atreid curse.
Adapted from Wikipedia, "Pelopia (daughter of Thyestes)" · CC BY-SA 4.0
I.Background
Thyestes and his brother Atreus had long fought for the throne of Mycenae; Thyestes had also seduced Atreus's wife Aerope. In vengeance Atreus killed Thyestes' sons and served them to him at a banquet. Thyestes swore revenge. An oracle then advised that if he had a son by his own daughter Pelopia, that son would kill Atreus.
II.Rape, recognition, and death
While Pelopia was staying at Sicyon at the court of King Thesprotus, she went to a riverbank to wash clothes stained with sacrificial blood. Thyestes, covering his face, attacked and raped her. She pulled out his sword and kept it so she could recognise her offender.
Soon after, Atreus came to Thesprotus searching for Thyestes; taking Pelopia for Thesprotus's daughter, he asked for her hand, and Thesprotus consented so as not to reveal the truth. Already pregnant by Thyestes, she gave birth to Aegisthus and abandoned him. A she-goat suckled the infant; a shepherd found him and gave him to Atreus, who raised him as his own.
Grown, Aegisthus was sent by Atreus to kill the captive Thyestes. He carried the sword Pelopia had once taken; Thyestes recognised it and asked about it. Pelopia was summoned, told how the weapon came to her, recognised Thyestes as her rapist, and stabbed herself with her father's sword. Aegisthus then killed Atreus and restored the kingdom to Thyestes.
III.Homonyms
Another Pelopia appears in myth as a daughter of Pelias (treated separately in this atlas as pelopia-pelias). This article concerns only Thyestes' daughter, mother of Aegisthus.