Clytemnestra's importance in Greek mythology comes from her marriage to Agamemnon, Menelaus' brother. There are two versions of Clytemnestra's involvement in the death of Agamemnon. Homer describes Agamemnon's departure for the Trojan War, to help to avenge his brother Menelaus. While Agamemnon is away, Aegisthus plotted to seduce Clytemnestra and murder Agamemnon once he returned from the Trojan War. As the years passed, and there was no word that the war was anywhere near an end, Clytemnestra weakened and welcomed the sensuous advances of Aegisthus. When the war does finally end, Agamemnon arrives home to be killed by men hired by Aegisthus. Orestes, Agamemnon's and Clytemnestra's son, kills Aegisthus to avenge his father's death. Clytemnestra disappears or is killed but Homer does not go into to much detail about her. In this version, Clytemnestra is weak and insignificant compared to the male players.
Aeschylus series of plays called Orestia provide the most popular version of this myth. In the first play, Agamemnon, Aeschylus describes Clytemnestra as a strong woman and not the weakling she appeared to be in Homer's version. When Agamemnon leaves for the Trojan War, Clytemnestra starts her torrid affair with Aegisthus. Together, they plot to kill Agamemnon as soon as he returns from the war. When the signal is given that the war is over, Clytmnestra prepares for the return of Agamemnon. She is already mad at Agamemnon for sacrificing their daughter, Iphigenia, and then she finds out that Agamemnon is bringing home another wife, Cassandra. As soon as Agamemnon's chariot pulls up in front of the palace, Clytemnestra goes out to welcome Agamemnon. She lays a purple cloth on the ground for him to walk over, at first Agamemnon refuses to walk over the cloth but soon gives in to Clytmnestra's request. Cassandra, given the sight of prophecy by Apollo but with the curse that no one would believe her because she failed to keep her promise to have sex with him, remained outside because she could see the doom surrounding the palace. When Cassandra finally enters the palace, a cry is heard and a blood drenched Clytemnestra is shown standing over the dead bodies of Agamemnon and Cassandra. Aegisthus marries Clytemnestra to become King but is no more than a puppet to Clytemnestra. This ends the play Agamemnon.