The correct answer is Aegisthus.
According to this myth, Thyestes was the king of Olympia who killed his own half-brother Chrysippus, along with his brother Atreus, and for that, they were exiled by their father, Pelops. Atreus later took the throne, even though Thyestes was supposed to, and during the feast, he served Thyestes his own children he previously cooked. Therefore, it was prophesied that Thyestes' son would kill Atreus, which was what happened. Aegisthus, Thyestes' son, did kill him in the end and avenged his father for the Banquet.