Agamemnon (Morshead Translation) by Aeschylus

The Oresteia is a trilogy of Greek tragedies written by Aeschylus concerning the end of the curse on the House of Atreus. The name derives from the character Orestes, who sets out to avenge his father's murder. The only extant example of an ancient Greek theater trilogy, the Oresteia won first prize at the Dionysia festival in 458 BC. When originally performed, it was accompanied by Proteus, a satyr play that would have followed the trilogy. Proteus has not survived, however. In all likelihood the term "Oresteia" originally referred to all four plays; today it generally designates only the surviving trilogy. Many consider the Oresteia to be Aeschylus' finest work. Principal themes of the trilogy include the contrast between revenge and justice, as well as the transition from personal vendetta to organized litigation....The play Agamemnon (Ἀγαμέμνων, Agamemnōn) details the homecoming of Agamemnon, King of Argos, from the Trojan War. Waiting at home for him is his wife, Clytemnestra, who has been planning his murder, partly as revenge for the sacrifice of their daughter, Iphigenia, and partly because in the ten years of Agamemnon's absence Clytemnestra has entered into an adulterous relationship with Aegisthus, Agamemnon's cousin and the sole survivor of a dispossessed branch of the family (Agamemnon's father, Atreus, killed and fed Aegisthus's brothers to Aegisthus's father, Thyestes, when he took power from him), who is determined to regain the throne he believes should rightfully belong to him. - Summary by Wikipedia