I was wondering, does anybody recognize the symol at the end of the E3 2012 stage demo when it says “an Ancient Evil Awakens” and a voice says " I have long dreampt of this day reclaimer". the symbol looks familiar but i cant remember what its for.
It’s the symbol for the didact.
this is the Didact
He is a forerunner commander who was the one who activated the Halo array.
He is mentioned in the Halo 3 terminals
The Didact 
thats it. i knew i had seen it before. it would be cool to see him and maybe Mendicant Bias since he is supposed to be still alive.
Aloso ,thanks for replying so fast.
Although the symbol towards the end of the E3 video was most definitely the Didact symbol (with a few minor changes), I highly doubt he will be the main enemy, this ancient evil. This is because throughout the books in which he is seen, he remains relatively benign and even shows regret towards his actions against humanity. I’d be willing to bet the precursors will come into play as the enemy, and the Librarian may enter as an ally.
Dont think he will be either, if i remember correct he never was said to be evil ,though prone to violent fits of rage, but that he wanted to protect humanity and the forerunner mantle. I also think that the prometheans will end up not being the ancient evil, because they are only a sort af a security system that will eventually recognize the humans and help them. also if you will notice, in the demo it appears that they go from being orange to blue/white like the normal forerunner look. Maybe they are corrupted and you have to fix that. i also think that the precursors will be the main enemy even if they are not introduced in halo 4.
The only characters from the Forerunner books that are described as Evil are the Pimordial and the Master Builder. We know what happened to the Primordial, but not the Master Builder.
I say he ended up in a Cryptum, and is back now.
Also, since the symbol is not quite the same as the Didacts, what if it is the MB’s symbol? Didact was head of the military, MB head of the builders.
As near as I can tell, the symbol is remarkably similar to the Didact’s, but is flipped upside down. I say this because of the edition of the Halo Encyclopedia that I have, and I feel that perhaps this represents a different person. A rival, an enemy. Symbols being flipped and mistaken for other things has already been demonstrated in the Halo universe. This symbol might perhaps represent the master builder, perhaps someone else. Also, as has already been noted, the Promethean defensive AI’s are orange. Normally, warm colors in an AI represent corruption. We have seen corruption of forerunner AI systems multiple times. I think it is perhaps either, the master builder, or someone else, possibly 05-032 MENDICANT BIAS [MB.05-32]. Who has taken control over Requiem. We have seen events like this happen before, in Primordium. That entity, wanting to exact revenge, may have hate for humans, The Didact or Librarian, or all life. We do not know. Cortana, nearing rampancy. Says,“I will not allow you to leave this planet!” (Maybe not an exact quote, I’m going from memory) It can be assumed, that this new enemy intends to leave the planet, to destroy -possibly- humanity or all races, maybe specific targets. The normally colored Promethean Defensive AI would appear to be on our side. We can assume, that either we take back control somehow, or something was already waring on this planet, and had these apparently friendly AI already. Perhaps the entity that has taken control of Requiem simply is not powerful enough to take control of all of it. A meta-class AI (Mendicant and Offensive Bias are two examples) could only control 5 Halo Rings at a time. That’s why we only have 7 rings, the other 5 have gone missing. They have either been destroyed, which is possible, or this new enemy might posses them also. But, “You have already said a meta-AI can only control so much.” you say. Well that’s true, but every Halo had a monitor. Corrupt a monitor to be on your side, like the Flood did with Mendicant Bias, and now you control the entire thing, by manipulating a thing of much less scale. But also, we don’t know where the Shan 'Shyuum (prophets) went to. They most certainly could hold a grudge. Humanity took away their power. They were forced into hiding, where? We do know that Mendicant Bias (or a fragment of him, at least) is still around. We was on the Dread Naught, trying to escape, but failed due to the Lekgolo in charge of cleaning the ship. He was formally disconnected by The Prophet of Truth. We can assume, that another Prophet has him now. Maybe they made it to Requiem, after all, some Covenant was there already (In a state of disarray, commonly noticed in an emergency evacuation.), and there is at least one new Covie weapon. We all know the San 'Shyuum were essentially the designers and developers of all their tech.
> As near as I can tell, the symbol is remarkably similar to the Didact’s, but is flipped upside down. I say this because of the edition of the Halo Encyclopedia that I have, and I feel that perhaps this represents a different person. A rival, an enemy. Symbols being flipped and mistaken for other things has already been demonstrated in the Halo universe. This symbol might perhaps represent the master builder, perhaps someone else. Also, as has already been noted, the Promethean defensive AI’s are orange. Normally, warm colors in an AI represent corruption. We have seen corruption of forerunner AI systems multiple times. I think it is perhaps either, the master builder, or someone else, possibly 05-032 MENDICANT BIAS [MB.05-32]. Who has taken control over Requiem. We have seen events like this happen before, in Primordium. That entity, wanting to exact revenge, may have hate for humans, The Didact or Librarian, or all life. We do not know. Cortana, nearing rampancy. Says,“I will not allow you to leave this planet!” (Maybe not an exact quote, I’m going from memory) It can be assumed, that this new enemy intends to leave the planet, to destroy -possibly- humanity or all races, maybe specific targets. The normally colored Promethean Defensive AI would appear to be on our side. We can assume, that either we take back control somehow, or something was already waring on this planet, and had these apparently friendly AI already. Perhaps the entity that has taken control of Requiem simply is not powerful enough to take control of all of it. A meta-class AI (Mendicant and Offensive Bias are two examples) could only control 5 Halo Rings at a time. That’s why we only have 7 rings, the other 5 have gone missing. They have either been destroyed, which is possible, or this new enemy might posses them also. But, “You have already said a meta-AI can only control so much.” you say. Well that’s true, but every Halo had a monitor. Corrupt a monitor to be on your side, like the Flood did with Mendicant Bias, and now you control the entire thing, by manipulating a thing of much less scale. But also, we don’t know where the Shan 'Shyuum (prophets) went to. They most certainly could hold a grudge. Humanity took away their power. They were forced into hiding, where? We do know that Mendicant Bias (or a fragment of him, at least) is still around. We was on the Dread Naught, trying to escape, but failed due to the Lekgolo in charge of cleaning the ship. He was formally disconnected by The Prophet of Truth. We can assume, that another Prophet has him now. Maybe they made it to Requiem, after all, some Covenant was there already (In a state of disarray, commonly noticed in an emergency evacuation.), and there is at least one new Covie weapon. We all know the San 'Shyuum were essentially the designers and developers of all their tech.
Thats my theory as well.