Aegisthus

Aegisthus was the son of Thyestes (the exiled king of Mycenae) with his own daughter, Pelopia. He was abandoned at birth, and raised unknowingly by his uncle Atreus (the usurping king of Mycenae), whom he later killed at Thyestes' request. While Atreus' sons Agamemnon and Menelaus were absent during the expedition against Troy, Aegisthus seduced Agamemnon's wife Clytemnestra, and effectively ruled with her as king of Mycenae. On Agamemnon's return, Aegisthus and Clytemnestra treacherously murdered him, and they continued to reign over Mycenae until Agamemnon's son Orestes avenged his father's death by killing them both.