Aegisthus, son of Thyestes, was a central figure in the bloody internal feuding of the Tantalid family. Thyestes and his brother Atreus had long battled over the throne of Mycenae; once Aegisthus was fully grown, he helped his father kill Atreus. The father-son duo briefly ruled over Mycenae before being driven out by Atreus’ son Agamemnon.
Years later, Aegisthus returned to Mycenae while Agamemnon was off fighting at Troy. He seduced Agamemnon’s wife Clytemnestra, and together they slaughtered Agamemnon once he was back from the war. Aegisthus and Clytemnestra then ruled Mycenae together until Agamemnon’s son Orestes killed them both to avenge his father.
The tale of Aegisthus was quite popular in ancient literature and art. Aegisthus himself was almost always imagined as a treacherous and cowardly character.