As someone who didn't trust Elidibus from his first cutscene, questioned every word he said, and called him "a snake" for years in the long-con hope that I would get to connect it somehow to the thirteenth zodiac and have a longitudinal brick pun land in the end, I feel uniquely qualified to make everyone who likes Elidibus angry at me all over again by answering this question.
Long story short: he lied.
Now let me admit right now that depending on how rigidly you want to define the word "lie", an argument could be made that Elidibus quite rarely did so. Rather, what he did most of the time was give his pawns just enough information to want to trust him and do what he says (because who else is giving out accurate, actionable intel?) ... but without enough context for them to realize that trusting him and doing what he says is in every way against their own best interest.
Example: If you are in a situation and there are five roads you could take - three to doom, one to Elidibus's best interest, and one to your best interest, Elidibus is going to tell you there are two roads out of this situation: doom or his best interest, which, according to him, just happens your best interest, too, so why not work together this time? The fact that you have a better option? You don't need to know that. That'd just complicate things. You need to shut up and help him accomplish his goals until he discards you like the worthless chess piece you are.
A REALM REBORN
The first thing that really put me off about him was that he acted in 2.1 to Minfilia and the Warrior of Light like he knew Lahabrea was a problem, then went right back to work alongside him doing exactly the same kind of stuff he was doing before. If anything, he was babysitting him to make sure he toed the company line without getting distracted. The problem for me was that apparently the company line was the same stuff he was doing before, but more efficient. Moreover Nabriales calls him out for visiting the Warrior of Light without telling anyone and Elidibus is like, "Chill. Zodiark just gave us different missions. We're on the same page."
This is a good time to point out that back in the A REALM REBORN era it doesn't look like SE had much of a solidified plan for these guys, yet, so who knows what the devs thought he was really alluding to there at the time (if anything). First and foremost, if you go back and look at those cutscenes, there are fourteen overlords PLUS Elidibus (and recall that now we know Emet-Selch was supposedly sleeping, and Azem was never raised, so who the seventh hell are these three extras?). Nabriales (in Japanese) acts as though there are only two Originals at this time, Lahabrea and Elidibus, while everyone else was resurrected within a shard they were assigned to, so I think a lot changed behind the scenes as they worked out who the Ascians "really" were and what they "really" wanted.
So anyway, Elidibus keeps being mysterious and helping Lahabrea set up what we later learn is Project Thordan.
The line that plagued me throughout this era was when Elidibus told Minfilia we would be "of one mind" if we knew the "true power of the echo".
But then...
HEAVENSWARD
Elidibus mostly takes a back seat for the Heavensward MSQ as Igeyorhm is assigned to help Lahabrea execute the final stages of the plan.
I suspect that at this stage of the game, SE planned to find excuses for the Ascians of "the other shards" to come here only to get ganked, but slowly abandoned the idea that there was one for each world because killing them was going way too slow.
But then what happens at the end of Heavensward? Lahabrea gives a rant about "the true power of the Echo" and becomes "of one mind" with Igeyorhm. Elidibus may not have lied, according to some, but he sure didn't tell the truth! This is when I decided he was "a snake". Why? Because I didn't trust him, anyway, but then Unukalhai came into the picture, and he's named after a star in the constellation that is the serpent in the 13th zodiac's grasp. I felt like I was setting up the best brick pun of all time, but ... it only ... really kinda 50% played out. It wasn't very satisfying if we're being honest. But I'm getting ahead of myself.
Lahabrea's "crowning act of idiocy" is that he expects Thordan to take the primal-binding, dragon-enslaving tech of Allag and gleefully go home to start building the Holy Ishgardian Empire as God King Thordan (thanks for figuring out incarnate summoning, Nabriales, sorry about being dead, but it's your own fault). Now that primal should have been well within the Ascians ability to control. Sure, he'd kill all the dragons and temper a bunch of people - because they can't all be at war if they're all tempered to love just you - but then Garlemald could invade, the war would escalate, someone would trigger a calamity and the Ascians win again.
Except he didn't. He whipped out Nidhogg's "long-lost" eye and transformed it into a sword-vessel capable of drinking the Warring Triad's nigh infinite power so he could destroy the Ascians himself along the way to building his empire. (Not a bad plan, really!) But you kill Igeyorhm, Thordan kills Lahabrea, you kill Thordan before he can fully drink the Triad, and now Elidibus is left with a big freakin' mess.
An aside, but I'm kinda surprised SE didn't explicitly go back and clean up that, during the cutscene where Elidibus realizes all of this, he really - really - doesn't seem to care Lahabrea's dead. At all. AT ALL. I'm sure given what we know about his state, we could make a number of excuses for him, but that SE didn't clean it up is surprising to me.
So now Elidibus is in a pickle. He was trying to balance Light and Dark on the Source so he can trigger a calamity and Thordan just woke up three very powerful primals that are going to stomp all over his perfectly-balanced chessboard. So he reaches into his bag of tricks and thaws out Unukalhai, a Warrior of Light (the regular kind, not the Champion kind, as far as we know, I think) from the fall of the Thirteenth. Why? Because he if shows up right now asking the Warrior of Light to just shut up and cooperate, he's probably gonna have some freakin' questions, and he does not have time for that. But a child with a sob story about how he didn't accumulate enough friendship to kill god like a real Final Fantasy hero would? Warrior of Light's not asking him anything but, "Are ya ready to start winnin' son?" And while they're off doing their thing the kid can hopefully put some good PR in for Elidibus.
But here's the thing about Unukalhai...
Go back and watch the Warring Triad cutscenes again. That kid spends the entire questline sparring with Regula and talking trash about Garlemald because they're causing the very problem they claim to be trying to eradicate. If they want to stop the summoning of primals and bring peace to the Three Great Continents, their overall plan for accomplishing that is as bad as their results so far. Think about that in context of what we know today.
Elidibus might have had a spark of sympathy for the kid given that he, too, was once a child in a situation bigger than he was ready for (I'm not sure the devs knew that yet, but let's go with it). But he could have told Unukalhai at any time that Garlemald was run by his BFF, who was acting under his orders. He didn't tell that kid jack except what would make him a useful pawn just like everyone else.
So then the WARRIORS OF DARKNESS show up, and this is the classic Elidibus. He tells them only what they need to know to conclude it's in their best interests to try to Rejoin the First without giving them any of the context they'd need to realize that's a terrible idea. Urianger has to bring that plan down from within himself, using methods that made more than few fans angry at him for not giving Minfilia informed consent about how her life was going to turn out. (She forgives him, but still, DANG.) Urianger admits he would have made a great Ascian if he didn't have the one thing that prevents him from being a useful pawn: faith that there's always a better way, instilled in him by the Warrior of Light.
This is where I was sure that Elidibus does care about balancing Light and Darkness but only insofar as ensuring the Rejoining. He's loyal to Zodiark, but even Zodiark doesn't want a Flood. Balance matters. (Kinda.) Then the lore book came out and helpfully clarified that Elidibus's "loyalty to Zodiark is absolute", so what little willingness I had to doubt my course for the most part EVAPORATED.
Tangential rant, this is why I love Ilberd as a villain. Ilberd lied to my face TWICE and I bought it TWICE. There's a quest called "Traitor in the Midst" and the preview is a picture of Ilberd, and I was like "I KNEW IT, ILBERD'S A TRAITOR. THIS IS SUBTLE FORESHADOWING." but then we rooted out the Ivy and Ilberd said he'd rather cut off his own arm than betray a friend. And I bought it. And I hated him for it. And then he came back as the Griffin, and it was obvious that he was the Griffin, but Ilberd looked Elidibus dead in the eye and said he was trash because he fills his pawns with lies and false hopes and sacrifices them for nothing, whereas he was giving his pawns everything they wanted. And I cheered him on! And then he did exactly the same thing! HE GOT ME AGAIN. Man, I love how much I hate that guy.
STORMBLOOD
I don't think there's a lot to talk about here. Elidibus was pretty openly lying about some stuff by now, but he was clearly just setting Varis up to think it was in his own best interests to temporarily sacrifice two cities so he could gain the technology and status quo required to dominate the world, using his own unfit-to-rule-son as a lab rat, when really all they were doing was giving Eorzea time and opportunity to establish a military alliance capable of making Varis desperate enough to use Black Rose and trigger the calamity. Elidibus claimed he didn't care if Varis killed the Ascians in black, but even that wasn't really a lie, as part of Fandaniel's book of grievances is that Elidibus treated him like he was expendable. We know now that he cared about Emet-Selch's death (kinda, we'll get to that), but the others not so much. Classic Elidibus.
SHADOWBRINGERS
We spend most of the set-up with Emet-Selch, but when we finally kill him, he has a moment of clarity and asks us to remember the Ancients and how much they loved their world, not just the Ascians they became and the atrocities they committed. This was also partly a message to Elidibus, Emet-Selch realized in his final probably-untempered moments that their plan had gone awry before even the Great Sundering, and that we might be worthy inheritors of the world after all.
Elidibus, probably still quite tempered (if we want to call it that; I mean he's according to Y'shtola a primal-esque being, so he can't be anything other than what he was summoned to be, which is not unlike what Zodiark would temper him to be, so...whatever it's moot for these purposes, lol.), is furious about this. Depending on the language play the game in, Elidibus straight-up says that his job is to make sure people think the right way, that he would have put Emet-Selch back in his place, and that if Emet thought for a single moment that Elidibus would ever work with you or cede his mission, he was "unworthy of the name Original" and even if it were his dying wish, he denies it.
I literally cheered - outloud - when Elidibus said there was never any common ground to be found between us. I was so worried it wouldn't all pan out in a way that made sense to me, and that moment was perfect. Elidibus and Emet-Slech made a FANTASTIC case for why they did what they did, and in the end a HORRIBLE case for that we should let them do it.
In his final, probaby-un"tempered" moments, Elidibus realizes that there is nothing left to fight for, and the mission had probably failed before it had even truly begun. Now, I think the line "The rains have ceased, and we have been graced with another beautiful day. But you are not here to see it." is perfect. It's beautiful. It's devastating. However, there is another way he says it that I think makes it even clearer where he's coming from: "My friends, how could I have been the last to go? To abandon you all to linger here as you went on alone?"
SO, in the end Elidibus ended up being pretty consistent after all for a character that had ... like, no flavor at all for like, many years. He did care about balance: the balance needed to complete the rejoining, kill the sundered, restore the Source, bring back Zodiark, sacrifice a ton of living things, and resurrect his brothers.
The greatest tragedy of Elidibus is that his one job was to chart the best course forward for his people, arbitrating disputes by being able to foresee outcomes, and all his great talents were weaponized by his accidental tempering to serve Zodiark alone, and he never. put it. together. Until his last moments, He thought his predicting of outcomes and manipulating people and sacrificing pawns was the right thing to do, and after all this unpleasantness his friends smiling faces would be staring back down at him and this nightmare would finally end.
So when it comes to everything we thought we knew about him, he lied.
And he meant well.
But he was wrong.