Euripides probably produced his Electra sometime around 420 B.C. In it Orestes, son of Agamemnon and Clytaemestra, returns home secretly to Argos. Apollo has ordered him to avenge his father’s murder by killing the murderers, Orestes’ own mother and Aegisthus, her new husband. Aeschylus had treated the same story in his Libation Bearers (Choephoroi) and Eumenides, the second and third plays of his Oresteia trilogy. Sophocles, too, wrote an Electra, which could equally well have preceded or followed Euripides’ play. Sophocles’ play can be mostly left to one side: Euripides shows himself aware of Aeschylus throughout, but his Electra shows few if any debts to that of Sophocles.
Kovacs, David. "Electra". The Literary Encyclopedia. First published 29 March 2011
[http://www.litencyc.com/php/sworks.php?rec=true&UID=13362, accessed 26 October 2016.]