Agamemnon, in Greek legend, was king of Mycenae and leader of the Greeks in the Trojan War. He was a son of Atreus and the brother of Menelaus, king of Sparta. After Atreus was murdered by his nephew Aegisthus, Atreus' brother Thyestes seized the throne of Mycenae, and Agamemnon and Menelaus fled to Sparta. There, Agamemnon married Clytemnestra, daughter of King Tyndareus, who bore him a son, Orestes, and three daughters, Iphigenia, Electra, and Chrysomethis.
Menelaus became king of Sparta and married Helen, who was abducted by Paris, the son of King Priam of Troy. When Priam refused to order Helen's return, the Greeks declared war on Troy, choosing Agamemnon as their leader.
The Greek fleet was held up at Aulis by adverse winds sent by the goddess Artemis (Diana) because Agamemnon had killed one of her favorite deer. To appease Artemis and secure a favorable change of wind, Agamemnon agreed to sacrifice his eldest daughter, Iphigenia. At the last moment Artemis spared her.
As the Greeks won victories over Troy, they took many prisoners. Among these were the girls Chryseis, given to Agamemnon for his pleasure, and Briseis, given to Achilles. Chryseis was the daughter of a priest of Apollo, and when Agamemnon refused to release her for ransom, Apollo visited a plague upon the Greek camp. Forced to give her up, Agamemnon seized Briseis in her place. Achilles was infuriated and withdrew from the battle at Troy.
The war lasted 10 years. At the final victory over Troy, Agamemnon received Cassandra, daughter of Priam, as part of his spoils. Cassandra was a prophetess and warned Agamemnon not to return to Mycenae. He ignored her advice and on his first day home was murdered by his cousin, Aegisthus, who had taken Clytemnestra as his mistress. Seven years later Orestes, aided by Electra, avenged his father's death by killing Aegisthus and Clytemnestra.
Versions of the story are told in Homer's Iliad, Aeschylus' Oresteia, and in plays by Euripides.