Aegisthus

In Greek legend, the son of Thyestes; while Agamemnon was absent at Troy he became the lover of Clytemnestra. Together they killed Agamemnon on his return to Argos. Aegisthus was later killed by Orestes.

In Greek mythology, Aegisthus ("goat strength" — also transliterated as Aegisthos or Aigísthos) was the son of Thyestes and of his daughter, Pelopia. The advice was to father a son with his own daughter, Pelopia, and that son would kill Atreus. Atreus, not knowing the baby's origin, took Aegisthus in and raised him as his own. When Aegisthus reached adulthood, Thyestes revealed his true parentage, that he was both father and grandfather to Aegisthus, who then killed Atreus and seized the throne.

Aegisthus and Thyestes ruled over Mycenae jointly, exiling Atreus' sons, Agamemnon and Menelaus to Sparta, where King Tyndareus gave the pair his daughters, Clytemnestra(often spelt Clitimneestra) and Helen, to take as wives. At his death, Tyndareus gave his throne to Menelaus, who then helped Agamemnon overthrow Aegisthus and Thyestes. After Agamemnon left Mycenae for the Trojan War, Aegisthus wanted to seduce his wife, Clytemnestra (mother of Erigone). as long as the singer was present, Clytemnestra resisted Aegisthus. Aegisthus then took the singer to a deserted island, and Clytemnestra was seduced. On the kings' return after the ten-year war, Aegisthus helped Clytemnestra kill Agamemnon (and his new concubine, Cassandra); Eight years later, Agamemnon's son, Orestes, and his daughter, Electra, returned to Mycenae and killed both Clytemnestra and Aegisthus.