<P> Atreus , Agamemnon 's father , murdered the children of his twin brother Thyestes and fed them to Thyestes after discovering Thyestes ' adultery with his wife Aerope . Thyestes fathered Aegisthus with his own daughter , Pelopia , and this son vowed gruesome revenge on Atreus ' children . Aegisthus successfully murdered Atreus and restored his father to the throne . Aegisthus took possession of the throne of Mycenae and jointly ruled with Thyestes . During this period , Agamemnon and his brother , Menelaus , took refuge with Tyndareus , King of Sparta . There they respectively married Tyndareus ' daughters Clytemnestra and Helen . Agamemnon and Clytemnestra had four children : one son , Orestes , and three daughters , Iphigenia , Electra and Chrysothemis . Menelaus succeeded Tyndareus in Sparta , while Agamemnon , with his brother 's assistance , drove out Aegisthus and Thyestes to recover his father 's kingdom . He extended his dominion by conquest and became the most powerful prince in Greece . </P>
who helped them recapture mycenae once they were old enough to fight
Aegisthus