Aegisthus (Ancient Greek: Αἴγισθος) is a central figure of the Atreid curse cycle: son of Thyestes by incest with Pelopia, usurper at Mycenae, lover of Clytemnestra, and co-murderer of Agamemnon. Homer's Odyssey and Aeschylus's Oresteia are the primary ancient portraits; after seven years of rule he is killed by Orestes in vengeance for Agamemnon.
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I.Family and early life
Aegisthus was the son of Thyestes and Thyestes's own daughter Pelopia — an incestuous union urged by an oracle so that the child would avenge Thyestes against his brother Atreus. In another strand he is the sole surviving son after Atreus slaughters Thyestes's children and serves them to their father.
Thyestes, battling Atreus for the Mycenaean throne and having seduced Atreus's wife Aerope, is tricked into eating his own sons. An oracle then advises him to father a son by Pelopia. He rapes her after a sacrifice, concealing his identity; she later takes his sword. When Aegisthus is born she abandons him in shame; shepherds raise him, suckled by a goat — hence the name. Atreus, ignorant of the child's origin, adopts him.
II.Death of Atreus
Pelopia gives the sword to Aegisthus; discovering it belonged to her father, she realises the incest and kills herself. Atreus sends Aegisthus to murder Thyestes, but the sword prompts recognition between father and son. Aegisthus returns and slays Atreus as he offers sacrifice on the seacoast. Father and son then seize the kingdom from which Atreus had expelled them.
III.Mycenae, Clytemnestra, and Agamemnon
Aegisthus and Thyestes rule Mycenae jointly and exile Atreus's sons Agamemnon and Menelaus to Sparta, where Tyndareus gives them Clytemnestra and Helen. After Tyndareus's death Menelaus uses Spartan power to drive out Aegisthus and Thyestes and place Agamemnon on the throne.
While Agamemnon is at Troy, Clytemnestra takes Aegisthus as her lover. On the king's return the pair murder him — some accounts give Aegisthus the blow, others Clytemnestra, avenging Iphigenia. Homer adds that Aegisthus posted spies, invited Agamemnon to a feast, and had him treacherously killed, even offering thanks to the gods for the success of his crime.
Aegisthus then reigns seven years. By Clytemnestra he has a son Aletes and daughters Erigone and Helen. In the eighth year Orestes returns, kills Aegisthus and Clytemnestra, and is pursued by the Furies for matricide. Aletes briefly holds the throne until Orestes returns and kills him; Orestes later marries Erigone.
IV.In drama and later culture
Homer gives almost no genealogy: after Thyestes's death Aegisthus rules Mycenae and takes no part in the Trojan expedition. In Aeschylus's Oresteia he is a lesser figure — appearing at the end of Agamemnon to claim the throne after Clytemnestra has done the killing, and dying quickly in The Libation Bearers. Critics call him a "weak lion" and a foil to Clytemnestra: cowardly, sly, full of threats, a tyrant in embryo who plots but does not act.
That feminised, decadent portrait shaped later art and opera: Seneca's Agamemnon, Strauss and Hofmannsthal's Elektra (a high, leaping tenor that squeals at death), and paintings such as Guérin's Clytemnestra and Agamemnon, where Aegisthus is a shadowy figure urging the queen forward. An ancient tholos at Mycenae is fancifully called the Tomb of Aegisthus (c. 1510 BC).