By the power of truth, I, while living, have conquered the universe.
Posted by: DonVinzone1
This.
Although the speculation part probably won't be about "the" Gravemind (the one we know), but "a" Gravemind.
The Gravemind at the time of Cryptum, Primordium and the third Forerunner book was most likely not the same phycical Gravemind as the one we know. That one was most likely destroyed when the Forerunners activated the Halos.
However, we know that the Prisoner/Gravemind was capable of surviving the test fire of Halo at Charum Hakkor. Halo doesn't affect Pure Form Flood, I'm not aware on any data to back me up with this statement but I doubt the Halos would kill off the final stage of the Flood evolution. After all, the Proto-Gravemind seemingly survived during Halo Wars along with the other Flood on the Shield World.
But because the Gravemind is like a living AI (or living database to be more correct I guess) that has, and builds upon, exsisting knowledge gained from the "database" build by previous Graveminds, he seems to actually be the ancient Gravemind.
Complicated story in short:
Physically not the same (probably)
but mentally he is (and expanded upon)
And because he has this knowledge of his predecessors he says stuff like "child of my enemy". Which we now know points at the ancient humans, and not to the Forerunners (who just adopted us as their heirs)
I'm not overly convinced about the Gravemind in Halo 2 and 3 being a different Gravemind. His appearance certainly does fit with the description of the Prisoner about being likened to a Eurypterid.
Just to back up the claim of Gravemind and the Prisoner being the same, there is irrefutable evidence.
Gravemind states in Human Weakeness that he has consumed many AIs but spared one who joined him, obviously referring to Mendicant Bias.
Primordium's description states that humans call the Prisoner "The Primordial", this is the same name Major John Smith uses to describe the Flood in The Mona Lisa.
The Prisoner is known as "the Timeless One", Gravemind describes himself as a "timeless chorus".
Gravemind states he has "listened - through rock and metal and time", the Prisoner listened to the humans and San'Shyuum at Charum Hakkor in his prison for a very long time.
The last words of the Gravemind is "resignation is my virtue; like water I ebb, and flow. Defeat is simply the addition of time to a sentence I never deserved... but you imposed." The latter part is referring to imprisonment, a sentence he never deserved. The PRISONER of Charum Hakkor, locked away for unknown reasons.
And the "child of my enemy" has already been pointed out referring to Ancient Humanity.
[Edited on 08.02.2011 6:00 AM PDT]