Atreus was a king of Mycenae in Greek mythology, son of Pelops and Hippodamia. He was married to Aerope and fathered a girl, Anaxibia, and two boys, Agamemnon and Menelaus, two of the protagonists of the Trojan War. All descendants of Atreus are collectively known as Atreidae.
Atreus and his brother Thyestes murdered their half-brother Chrysippus, in order to acquire the throne of Olympia. However, for their act, they were exiled and sought refuge in Mycenae, where their mother, also banished from Olympia, hanged herself. There, he ascended on the throne, but soon afterwards, Thyestes tricked him with the help of Aerope (who was his lover) and took the throne for himself. Atreus managed to retake the throne with the help of Hermes and Zeus, banishing Thyestes.
When Atreus found out that his wife had an affair with his brother, he decided to seek revenge. He killed Thyestes' sons and fed them to him. Thyestes asked an oracle for advice, and he was told to father a child with his daughter; that child would then avenge him. Thyestes slept with his daughter, Pelopia, and had a child, Aegisthus. Aegisthus was abandoned by his ashamed mother and was found by a shepherd, who then gave him to Atreus. When Aegisthus became an adult and was told the truth by Thyestes, he killed Atreus.