Who is The Chorus from The Oresteia and what is their importance?

The Chorus was a traditional element of Classical Greek theater, and consisted of a number of actors speaking with the voice, attitude and perspective of a single character. There are two important elements to note about the Choruses in The Oresteia. First, in each play the Chorus has its own identity: in Agamemnon, they are the old men of Mycenae; in The Libation Bearers, they are female Trojan prisoners-of-war/servants; in The Eumenides, they are the Eumenides themselves, primeval goddesses of ancient, natural law. It's important to note here that in original (Classical) performances, both male and female choruses would have been portrayed by male actors as would all the characters. The second thing to note is that the role played by the Chorus in the action of all three plays is significantly different from the role traditionally played by the Chorus in Greek theater. Usually, the Chorus merely observed and commented on the action of the play, rather than entering directly into it. While the Male Chorus in Agamemnon essentially follows true to this form, the Choruses in Libation Bearers and Eumenides function differently; they participate directly in the action and are actually characters involved in the story rather than merely observers and commentators.