Atreus was the son of Pelops and Hippodamia and the elder brother of Thyestes. He and Thyestes were banished from their homeland and migrated to Mycenae (according to some traditions, they were exiled by their father for murdering their half-brother Chrysippus).
Upon arriving in Mycenae, Atreus and Thyestes immediately coveted the throne. The earliest sources claim that Thyestes was named king, despite Atreus being the older of the two. But in what eventually became the more familiar tradition, Atreus and Thyestes vied bitterly for power.
Their feud turned into a years-long cycle of cruelty and retribution: Thyestes seduced Atreus’ wife Aerope to steal the golden lamb (which represented the claim to the throne), while Atreus went so far as to cook Thyestes’ sons and serve them to him.
In the end, Thyestes managed to kill Atreus with the help of his son Aegisthus. But Atreus was avenged by his sons Agamemnon and Menelaus (sometimes known as the “Atreids”), with Agamemnon ultimately becoming king of Mycenae.
Unfortunately, the atrocities carried out by Atreus and Thyestes were not forgotten by the gods, and the curse of the house of Atreus continued to haunt his descendants.