With so many of us picking up Halo 4 tonight, I thought it would be a good idea to post a few key story points from Halo's extended fiction, since I have a feeling they will play directly into what happens in the games from this point on. Of course, these are some heavy spoilers for some of the Halo novels (primarily the Greg Bear Forrunner Trilogy).
*** Regarding the Forrunners ***
Forruners were obviously technologically advanced. They also had EXTREMELY long lifespans (tens of thousands of years, easily). But they were not as far above humans as we (gamers) originally believed. In fact, they were once at war with Humans, over 100 thousand years before Halo CE. They defeated humans, but just barely. In fact, it is theorized that Humanity might have actually won the war, except we were ALSO fighting the flood at the same time.
In order to control humanity, the Forrunners wiped us out to the brink of extinction. Those who remaned were genetically debased back to a caveman state.
Forrunners themselves often wore advanced armor, each with its own built-in AI. This AI would often show itself as a small Blue Female. This ties in to the theory that Dr Halsey, the creator of the Spartan project, was deeply influenced by ancient Forrunner artifacts and technology that she had discovered. In other words, it is possible that Master Chief and Cortana are based very much on Forrunner technology.
*** The Didact ***
The Didact was actually introduced back in Halo 3, in the hidden terminals. He was the leader of the Forrunners armies, and helped them win the first war against humanity. Larger, stronger, and more powerful than most others of his kind, he is in a way the Forrunner equivelant of the Master Chief.
He was actually directly opposed to the creation of the Halo rings as a weapon to combat the flood. He proposed the construction of Shield Worlds in which the Forrunners could protect themselves through isolation. Requium is believed to be one such shield world. Because of his opposition to the creation of the Rings, the Didact was forced into exile by his rivals high within Forrunner society.
One more important fact about the Didact: There are 2 of him. Forrunner's version of "Puberty" involves a form of cross-mutation. A young forrunner will absorb the genetic imprint of one of his elders, taking on some of their memories, and even their physical appearance. Shortly before the initially firing of the Halo rings that wiped out most life in the universe, the Didact imprinted upon a young Forrunner named Bornstellar.
The Didact's genetic code was so strong and overpowering (since it contained tens of thousands of years of genetic code and memory) that young Bornstellar was virtually absorbed by it. Essentially, just before the firing of the Halo rings, there were 2 Didacts running around, 1 of whom used to be a different person. It is unknown if both Didacts survived the firing of the rings, or WHICH one of them meets Master Chief in Halo 4.
*** About AI ***
Forrunner society put great emphasis on the creation and use of AI constructs. Their ships had AIs, their armor had AIs, their homes and cities were run by AIs. But there was one AI that dwarfed all others: Mendacit Bias. MB was created by the Didact. It was far more complex and powerful than any other AI in existance. It was so powerful that it began to develop a level of self-awareness that was not intended. At one point, MB actually took control of a recently constructed Halo Ring and went all "broken arrow" with it, attempting to use it for its own purposes. It was re-captured by the Didact. It is unknown what happened to it after that.
So for Halo nerds like me, there is a clear mirror image beginning to develop between Humanity and the Forrunners.
Both sides are eager to establish themselves as the dominant power in the galaxy. Then we have Master Chief and the Didact: champions of thier people, but both potential outcasts as well. Are we going to see Chief go through a similar exile as the Didact? Will he go through similar transformations? And how will the AI play into this? Cortana is clearly being set up to mirror Mendacant Bias. What will happen when she decides to take matters into her own hands?