The story of Halo, as told in the mainline video games, isn’t exactly the most interesting tale ever told. The larger world, however, is fascinating; there’s a religious cult of aliens, a few different wars, an infectious race that threatens to destroy the universe, and a set of rings designed to destroy it all first. The games tend to stick to the here and now of where the main characters are standing or who they need to shoot.
Thankfully, Halo’s ancillary material — like books, comics, short stories, and data logs — helps fill out the background of the universe and explores the millions of years worth of history that lurks beyond Master Chief’s intergalactic travels.
For those who don’t have dozens and dozens of hours to spend (waste?) reading the books — which mostly have names like Halo: Cryptum — here’s an abridged version of what they contain. In other words, here’s all the cool stuff the games mostly don’t tell you about.
The creators of everything
Halo’s history starts with the Precursors, a group of technologically advanced, Lovecraftian beings who ruled the galaxy millions of years before the events of the games. The Precursors created both the Forerunners, the race of aliens the Covenant worship, and ancient humans (more on them later). The Precursors believed in an idea called the Mantle of Responsibility, which they felt gave them responsibility to protect all life in the galaxy — in part because they created most of it. As the Precursors’ civilization grew older, they planned to pass the Mantle on to humans. However, the Forerunners felt that the Mantle should belong to them, and so they began attempting to eradicate the Precursors in order to take control of the galaxy.
By this time, the Precursor society was already in decline and, despite their technological advantage, they began to lose the fight against the Forerunners. As the once-great civilization’s last hopes of winning the war grew dim, the Precursors became desperate to both wipe out the Forerunners and help themselves live forever.
In their desperation to achieve both ends, the Precursors accidentally (sort of) created the Flood, a dangerous parasite with a drive to infect all intelligent life. Because the Precursors were capable of changing forms over millions of years, some had assumed the form of tiny dust particles with plans to regenerate in the future. However, over thousands of years, these particles became corrupted, and eventually they transformed into the earliest forms of the Flood.
With their civilization essentially gone, the last remaining Precursors became obsessed with the Flood and began teaching it to ignore humans, as if they had a natural immunity, and to hunt down Forerunners instead. The utter destruction and ruin of the Forerunners became the remaining Precursors’ only mission in life, and technically, they succeeded.
The Flood are the only remaining legacy of the race by the time of the Halo games. In fact, Gravemind claims to be a Precursor but is actually the transferred consciousness of a Precursor called Primordial who helped to carefully orchestrate the fall of the Forerunners by convincing the race’s own AI to turn against them.
After the rule of the Precursors, the Forerunners took up the Mantle of Responsibility and became the watchers of the galaxy’s sentient life. But they weren’t the only advanced species that lived there.
The golden age of humanity
Halo’s prehistoric humans were brilliant and technologically advanced ancestors of the humans that exist in the game. They were capable of galactic travel and colonization, and for large portions of their history, they were close allies with the San’Shyuum — known later as the Prophets.
Eventually, humanity’s journey through the stars led them to the Flood, and war broke out almost immediately.
The humans and the San’Shyuum threw their collective might at the Flood, only for the infectious race to continue to spread across their various planets. Out of desperation to get ahead of the infection, humanity took over several Forerunner worlds. Eventually, the Flood simply stopped fighting and infecting humans — because of the Precursors’ actions described earlier in this story — and humanity survived their encounter.
And that’s when the Forerunners stepped in.
The human-Forerunner war
The Forerunners’ time as protectors of the galaxy was mostly marked by a series of tremendously incompetent decisions, including the way it dealt with humanity. After humans invaded a few Forerunner planets in an attempt to stop the Flood, the Forerunners dramatically overreacted. They assumed humanity was pushing toward war and decided humans must be stopped. It’s possible that one reason for the Forerunners’ overreaction here was because they resented the fact that humanity was the favored race of the Precursors and simply wanted them out of the way, but since Halo likes to keep at least a few mysteries around the Forerunners, we don’t know for sure.
The Forerunner-human war was more like an annihilation. Despite the fact that the humans had technology that rivaled, and in some cases even surpassed, the Forerunners’ tech, the human race had already been pushed to the brink of extinction by the Flood. Humanity, mostly fighting alone after the San’Shyuum surrendered early in the war, eventually got pushed back to their home world of Charum Hakkor. After a siege that lasted multiple decades, the humans were finally defeated.
Because the Forerunners refused to listen to humanity’s reason for taking the planets in the first place, or anything about humanity’s conflict with the Flood, they determined that humans were too dangerous to be permitted to continue to evolve. So in order to protect the rest of the galaxy under the Mantle of Responsibility, the Forerunners returned humanity to what they called Tier 7 technology. The Forerunners have a complicated tier-based ranking system for technology; Tier 7 is the lowest, describing Stone Age tech, and Tier 0 is the highest, which only the Precursors ever reached.
As a final act of bitter revenge against the Forerunners who wrongly wiped out their civilization, humanity destroyed all of its records of the Flood just before they were regressed.
After their conflict with the humans, the only race in the galaxy that could reasonably oppose them, the Forerunners enjoyed a long period of peace. In fact, things in the galaxy were so peaceful that the Forerunners actually de-weaponized completely. Which turned out to be a dire mistake with the Flood still around.
When the Forerunners first discovered the Flood, they assumed it to be an unintelligent disease, rather than a sentient race hell-bent on consuming all living things. Because of this assumption, they started by treating it as a medical issue that could be solved by quarantine, short-term treatment, and the search for a cure. This approach continued for over a hundred years while the Flood slowly took over more and more of the galaxy. By the time the Forerunners realized the truth, they were already late to a war that started a century ago, and they didn’t even have weapons to fight it.
Despite making some progress in weapon development and containment, the Forerunners really only managed to slow rather than stop the Flood’s progress through the galaxy. Finally the Forerunners realized that they had to find a larger, more apocalyptic solution. While there were major disagreements within the Forerunners’ ranks about the decision, they eventually decided to create the Halo array in order to destroy every living thing in the galaxy, with only The Ark acting as a life-saving vessel.
As the Flood takeover of the galaxy got progressively worse, the Forerunner known as the Didact (who both is and is not the antagonist from Halo 4) fired the Halo array, which worked ... mostly. It wiped out nearly all sentient life in the galaxy, and only a few Forerunners survived on The Ark.
The Forerunners left behind automatons like the Sentinels and AIs like 343 Guilty Spark to re-seed the galaxy with life, including humans and members of the Covenant, leading to the events of the first Halo game.
Halo has somewhere around 30 books out at the moment, with the latest being released in October 2021. Most of these books aren’t about the history of the galaxy and the Forerunners, but a few are. If you’re interested in learning more about what happened in Halo’s universe before the games, here are a few books worth reading.
The Forerunner Saga
Greg Bear’s trilogy of books is the most important place to start for any of Halo’s ancient history. This series of books covers the Forerunners and ancient humans, and it’s where almost all our information on those two civilizations, and the Precursors, comes from. These books are entertaining, but only if you’re really, really deep into the Halo nonsense, because they’re proper-noun soup and all the characters have names like Bornstellar Makes Eternal Lasting. (I enjoyed them very much.)
These aren’t really books, but the Halo 4 Terminals give you a bit of information about some of the most important characters in the Forerunner Saga. They also don’t mean much without the books to back them up.
Halo Mythos is a huge guidebook to the Halo universe and offers a timeline of the entire story (at least up until 2016). Only the first section is about the series’ ancient history, but it’s interesting and useful nonetheless.