Before you read, this thread contains spoilers from the Terminal on the CEA mission ‘The Maw’ and should not be read for those who have not yet found it!
If you did decide to read, you may want to watch the Terminal on The maw to freshen your memories.
In the final terminal, 343GS talks of how ‘Once I discovered our plan to save the galaxy succeeded, the Ancient Enemy is unleashed once more.’
This, to me points STRAIGHT towards the Flood. This is because the Flood was held captive and in stasis for 100,000 years, and were unleashed by the Covenant during the events of Combat Evolved.
Then again, maybe the Ancient Enemy is… us… We warred with the Forerunners for years, thousands of years ago, proving to be a danger and a challenge even with the Flood attacking us too. We were beaten and devolved, until a few thousand years later when we take to the stars once more. We still war with one and other and now with the Covenant too. This is shown by the animation of a battle. Finally, we now have the power and knowledge to govern the future of Halo. Whether we use them or destroy them is up to us, so maybe this could explain why we are referred to as ‘the Ancient Enemy’, as we foil the Forerunners plots once more and jeopardize their lives and their plans, like the ancient conflict 100,000 years prior to Halo: Combat Evolved.
Also, in another Terminal, Terminal 6 343GS says that the cure to the Flood was denied to them by their Ancient Enemy, and Ancient Humans were the only race with a cure…
Finally, the Ancient Enemy could be the ‘Promethians’ with their ‘trademark lethality’. however, The Librarian may have to prevent this ‘He’ (who is somehow connected with the Promethians) from unleashing his rage upon us. And apparently, we might even prefer the Flood, so… that’s not good.
So, according to the above paragraph, and the Terminal video the Promethians are still around, if you listen properly to 343GS’ dialogue.
So right there, there’s three possible candidates for the Ancient Enemy.
