There's a reason why most religions describe their gods as enigmatic, incomprehensible, ineffable, mysterious, baffling, or any number of synonyms you could fish out of a thesaurus. The Apollo of Aeschylus's The Eumenides is no exception. Really, the guy has more contradictions than you can shake a stick at. (Oh, and when we say "the Apollo of Aeschylus's The Eumenides," that's because we're going to be talking about the god as he appears as a character in the play; for more info on Apollo's role in Greek religion—which is very relevant to the play—you should check out this website.)
Let's start with what is least ambiguous about Apollo: his support for Orestes. A good case could be made that this support really is unwavering. Not only has Apollo been Orestes's guardian in the past, but his first words to Orestes in this play promise to look out for him in the future, too.
Once Orestes heads offstage on his journey from Delphi to Athens, Apollo immediately prays to his brother Hermes to give him safe passage. Then, when Orestes arrives in Athens, Apollo shows up not long afterwards to defend him at the trial.
So far so good. But it can't be denied that, even though Apollo has Orestes's back, he doesn't seem too concerned about how much Orestes will have to suffer in the meantime. Like, sure, maybe Apollo didn't want to transgress on the territory of his bro Hermes, who was the god in charge of travelers, but would it really have been that much trouble for Apollo to accompany Orestes on his journey to Athens and fend off those fearsome Furies for him?
The same goes for Apollo's fashionably late entrance to the trial, which is in good time as far as defending Orestes goes, but he's still left the guy to undergo the terrifying experience of being captured by the Furies' "binding song." Apollo's definitely sending some mixed messages here.
Apollo sends out even more mixed messages when it comes to the issue of telling the truth. For example, while he is acting as Orestes's defense attorney, Apollo freely admits that he was the one who told Orestes to kill his own mother:
(Apollo): "I have come both to give evidence—for this man is legally a suppliant and refugee at my hearth, and I am his purifier from bloodshed—and to support his case myself. I am responsible for the killing of his mother." (576-580)
He also says that he never used his oracle to prophecy anything that might be contrary to the will of Zeus:
(Apollo) (to the jurors): "I shall say to you, who are here by Athena's great ordinance, that [the blood of Clytemnestra] was shed justly; and as prophet I shall not lie. I never yet said at my prophetic throne, not about man, not about woman, not about city, except what Zeus the Olympian Father might command. I tell you plainly: understand how strong this just plea is, and heed the Father's will; an oath is in no way stronger than Zeus." (614-621)
Because Zeus is the god in charge of justice, this is basically Apollo's way of saying that everything he prophesied was in accordance with the truth of Zeus's will, and, because of that, totally just.
Once again, so far so good. But actually, it seems like Apollo doesn't have a big problem with playing fast and loose with the truth. Consider the final argument he makes in Orestes's defense, the killer argument that says that mothers aren't related to their children by blood. Now, this idea is pretty wacky in itself, but it actually also contradicts the argument Apollo made to the Furies earlier in the play. In Apollo's first confrontation with the Furies, he told them that they were making a mistake in thinking that husbands aren't blood relations to their wives, because the traditional marriage vows actually make them such:
(Apollo): "You quite dishonour the pledges given Hera and Zeus for a marriage's fulfillment! You make them of no account! Cypris too is rejected with dishonour in your argument, Cypris the source of what is dearest to mankind. A man and wife's marriage-bed once under destiny is greater than any oath, with justice as its guardian. If therefore you are lax in exacting payment from them when they kill each other, and in watching over them with your rancour, I say you are driving Orestes into exile unjustly." (211-221)
The proof of this, in Apollo's argument, is sex, which he refers to, metaphorically as "Cypris" (another name for Aphrodite, the goddess of sex). When he calls sex "the source of what is dearest to mankind" (216), he doesn't mean just sex itself, but also the children that result from it. (This is the interpretation of Christopher Collard, on p. 207 of his Oxford World's Classics edition of the play.)
But if marriage-vows make husbands and wives share the same blood, and that union results in children, wouldn't that mean that the children should be blood-relations to their mothers? This looks like Apollo is twisting his arguments around to suit the needs of the moment. This is starting to look like Apollo is more interested in "truthiness" than truth.
Actually, this whole bending the truth thing runs even deeper than that. First of all, notice that, when Apollo is talking about how his oracle reveals the will of Zeus, he doesn't say that his oracle reveals what Zeus does say, but rather "what Zeus the Olympian Father might command." (614-621) "Might"? What do you mean, "might," Apollo? So you didn't even check that stuff with him in advance? You just sit around guessing what Zeus might say and then base your predictions on that? Great. Real reassuring.
Also, think about it: if Apollo were so convinced that his case in favor of Orestes was totally airtight, he wouldn't have to make a big speech to Athena before the trial begins about all the awesome stuff he will make happen for Athens if Orestes gets off the hook. All these examples confirm that, even though Apollo is steadfast in backing up Orestes, he is something of a smooth operator. Does this mean that the Furies might have a bit of a point in accusing him of conspiring with Athena and the other younger gods to take power away from them and the other older gods?