Aegisthus (; ; also
transliterated as
Aigisthos) is a figure in
Greek mythology. He was the son of
Thyestes and his daughter,
Pelopia. The product of an incestuous union motivated by his father's rivalry with the house of
Atreus for the throne of Mycenae, Aegisthus murdered Atreus to restore his father to power. Later, he lost the throne to Atreus's son
Agamemnon.