a cousin to and the murderer of Agamemnon, whose wife Clytemnestra he had seduced. He usurped the kingship of Mycenae until Orestes, Agamemnon's son, returned home and killed him
Aegisthus in American English
(iˈdʒɪsθəs)
noun
Greek Mythology
the son of Thyestes and lover of Clytemnestra: he helps her to kill her husband, Agamemnon