Atreus, in Greek legend, the son of Pelops of Mycenae and his wife, Hippodamia. Atreus was the elder brother of Thyestes and was the king of Mycenae. The story of his family—the House of Atreus—is virtually unrivaled in antiquity for complexity and corruption. There are several different accounts of Atreus’s feud with Thyestes.
A curse, said to have been pronounced by Myrtilus, plagued the descendants of Pelops. His sons Alcathous, Atreus, and Thyestes set upon a bloody course with the murder of their stepbrother Chrysippus, the son of Pelops’s union with a nymph. After the crime the three brothers fled their native city of Pisa; Alcathous went to Megara, and Atreus and Thyestes stopped at Mycenae, where Atreus became king. But Thyestes either contested Atreus’s right to rule or seduced Atreus’s wife, Aërope, and thus was driven from Mycenae. To avenge himself, Thyestes sent Pleisthenes (Atreus’s son, whom Thyestes had brought up as his own and who does not figure in every version of the story), to kill Atreus, but the boy was himself slain, unrecognized by his father.
When Atreus learned the identity of the boy, he recalled Thyestes to Mycenae in apparent reconciliation. At a banquet Atreus served Thyestes the flesh of Thyestes’ own son (or sons), whom Atreus had slain in vengeance for the death of Pleisthenes. Thyestes fled in horror to Sicyon; there he impregnated his own daughter Pelopia in the hope of raising one more son to avenge himself. Atreus subsequently married Pelopia, and she afterward bore Aegisthus. Atreus believed this child to be his own, but Aegisthus was in fact the son of Thyestes.
According to one version of the story, Agamemnon and Menelaus—sons of Atreus and Aërope—found Thyestes at Delphi and imprisoned him at Mycenae. Aegisthus was sent to murder Thyestes, but each recognized the other because of the sword that Pelopia had taken from her father and given to her son. Father and son slew Atreus, seized the throne, and drove Agamemnon and Menelaus out of the country.