In the later part of his story Herodotus is dependent on the family traditions of Harpagus, whose treason is justified by the cruelty with which Astyages had treated him (the story of Atreus and Thyestes is transferred to them).
Atreus was murdered by Aegisthus, who took possession of the throne of Mycenae and ruled jointly with his father Thyestes.
His kingly office had come to him from Pelops through the blood-stained hands of Atreus and Thyestes, and had brought with it a certain fatality which explained the hostile destiny which pursued him.
Plutarch (Cicero, 5) mentions it as reported of Aesopus, that, while representing Atreus deliberating how he should revenge himself on Thyestes, the actor forgot himself so far in the heat of action that with his truncheon he struck and killed one of the servants crossing the stage.
Having murdered his stepbrother Chrysippus, Atreus fled with Thyestes to Mycenae, where he succeeded Eurystheus in the sovereignty.