The title of Aeschylus's The Eumenides is Greek for the "Kindly Ones." Who are the "Kindly Ones" in this play?
Maybe Athena and Apollo, because they help Orestes? Dead wrong. Don't worry, if you haven't read to the end of the play yet, we won't blame you for not knowing—because you'll never guess. The "Kindly Ones" named in the title of The Eumenides are actually the horrible Furies who pursue Orestes… after they undergo a magical transformation thanks to the goddess Athena. Huh? Well, the basic thing you have to remember is that The Eumenides is Part III of a trilogy of tragedies called The Oresteia.
Most interpreters of the trilogy as a whole think that its main theme is the development of society from resolving conflicts through revenge (i.e. more bloodshed) to resolving them through courts of law (i.e. peacefully). The Furies, who are essentially spirits of vengeance, have no place in this new order—at least not in their original form.
So, the transformation of the Furies into the Kindly Ones completes the thematic arc begun in Agamemnon and carried on in Libation Bearers. If you are approaching The Eumenides without having read those first two plays, we'd recommend that you give them a go to get the full experience.