Be Forerunner All This Started…
We begin with the Halo Forerunner books, set 100,000 years before the games begin. Bornstellar Makes Eternal Lasting, a young Forerunner (yes, that’s his actual name), is searching for Precursor artifacts when he comes across two humans, Chakas and Morning Riser. The two take Bornstellar to a ring island and end up activating the cryptum of the Didact, a Warrior-class Commander of the Forerunner military during the war against humanity and the San ‘Shyuum (Prophets) over Forerunner worlds. The Librarian saved humanity from extinction after the Forerunners lost the war.
The Didact conscripts Bornstellar, Chakas, and Riser as his makeshift crew and slowly uploads his mind into Bornstellar’s body. The young Forerunner learns that his father helped create the Halos intended to wipe out the Flood, but Didact opposed this weapon and was exiled. The four visit the Prophet homeworld, where they’re captured by Builders (creators of the Forerunner megastructures) and brought to trial. Medicant Bias, a Forerunner AI, turns on the Forerunners and wants to use the combined Halos to start wiping out all Forerunners. Several Halos are able to escape through failsafe protocols, and Bornstellar ends up on the Ark, where he meets the Librarian and learns the Didact has been executed…or so they think. With his mind fully uploaded into Born’s body, it’s revealed that an escaped prisoner, the Primordial, is the last surviving member of the Precursors, who were killed by their Forerunner creations. And he is pissed.
Didact later returned to the artificial world Requiem to continue his mission against the reemerging Flood. Furious with his obsolete strategies now that a Gravemind (the ultimate and final form of the Flood) had learned all his tactics, Didact acquired a Composer that Forerunners used to convert their physical bodies to digital form. He used the Composer to transfer his Prometheans’ biological forms into war machines, turning them into Promethean Knights. Once the Knights eradicated the Flood, they’d set their sights on humanity and any other race that could threaten his kind. The Librarian sealed him in a Cryptum in the heart of Requiem so that his mental damage at the hands of Gravemind could be healed by the Domain and he would help humanity ascend to become the caretakers of the galaxy with the Janus Key. Instead, the Didact would spend the next 100,000 years stewing in his rage and insanity.