Horizon Zero Dawn: HADES, the World-Ending Supercomputer, Explained
Alex Lukas
WARNING: The following contains spoilers for Horizon Zero Dawn.
In Horizon Zero Dawn, Aloy travels in search of the secrets behind the robotic creatures which stalk the lands. It's no easy feat for her, as it entails venturing deep into dark underground chambers, ascending to the peaks of derelict skyscrapers and coming face-to-face with an enemy bent on extinguishing humanity itself: HADES.
HADES is Aloy's primary antagonist, functioning as the final boss of the game as well as a harbinger of what she'll be up against in later games in the series, such as the upcoming Horizon Forbidden West. Aloy doesn't understand what HADES is or why it exists until late into the story, yet what she uncovers has the power to alter literally everything. But perhaps more interesting than what we know about HADES is what we don't know. HADES has a complex origin, and for all that its machinations are ultimately thwarted by Aloy, it is merely one piece in a much larger puzzle.

A GAIA Subordinate Function

HADES was originally a subordinate function of a greater AI known as GAIA. Tethered to the directives of GAIA like all nine of the subordinate functions, HADES was a tool in an unimaginably advanced technological attempt to prevent all life on Earth from being consumed by the war machines known as the Faro Swarm. This was an attempt which understood that, in many ways, humanity had already lost.
The Faro Swarm was capable of exponentially replicating, consuming biomass as fuel, and hacking enemy military equipment to the extent that humanity could not mathematically hope to contain it. All soldiers on Earth perished in a futile battle against them. Dolphins and entire forests were consumed by the robots as fuel, and every last remnant of biomatter the robots could detect was obliterated until the planet was a barren husk of itself. No living species existed on Earth by the end of the twenty-first century.
Thanks to Project Zero Dawn, however, the world's scientists had come together to create a chance of someday restoring the planet -- the most advanced AI in all of human history, GAIA. The AI was a central administrator which governed nine subordinate functions using a combination of intelligence, ethics and empathy. The subordinate functions themselves were designed to slowly work to defeat the Faro Swarm and terraform the Earth. MINERVA functioned to brute force the Faro Swarm deactivation codes; AETHER and POSEIDON functioned to detoxify the atmosphere and oceans, respectively; HEPHAESTUS functioned to manufacture terraforming robots at Cauldron sites; DEMETER and ARTEMIS functioned to reintroduce flora and fauna genetic stock to the Earth; ELEUTHIA functioned to reintroduce and raise humans through cloning genetic stock; APOLLO functioned to educate new generations of humans; and HADES functioned to reverse unsuccessful terraforming attempts if the new biosphere was deemed unsuitable for sustaining life.
Reversing GAIA's terraforming was a method of last resort meant to return the Earth to a sterile state and extinguish all existing life in order to start the terraforming process anew. HADES was thus the deadliest of the nine subordinate functions, and the only one that remained functional yet inactive, unneeded because GAIA's first attempt at terraforming was completed successfully. Until the day a mysterious signal was transmitted.

Rogue Machinations

Approximately one thousand years after the fall of humanity and GAIA's creation, a mysterious signal was transmitted to the facility which housed GAIA. The signal is of unknown origin, however, it resulted in the unshackling of the nine subordinate functions from GAIA's control, allowing them to act under their own independent authority. The rogue HADES sought to execute its destructive purpose, resulting in the events of Horizon Zero Dawn. It cared nothing for the fact that the GAIA terraforming project was successful.
Manipulating a wandering scholar named Sylens and an exiled tribe known as the Shadow Carja, HADES plotted to access a MINERVA spire by bringing the surrounding lands under its control. MINERVA spires are advanced signal towers used to broadcast the deactivation codes to the Faro Swam. HADES came close to reversing these deactivation codes to reawaken the Faro Swarm, bringing about the second biological death of Earth.
Luckily, Aloy was able to avert this calamity by the skin of her teeth. As the clone of Dr. Elisabet Sobeck, she had the genetic fingerprint required to unlock control room of the GAIA Prime facility and activate the master override. This was an effective kill switch for GAIA or any of her subordinate functions, and the one thing left in the world capable of stopping the rogue HADES.

Current Status

At the end of Horizon Zero Dawn, it seemed HADES was destroyed. Yet a post-credits scene proved quite the opposite and, in the process, hinted at the greatest mystery of the series. HADES was captured by Sylens, and in a condescending taunt to the rogue subordinate function, he tells it, "We've still so much to discuss, so much you never revealed. Your Masters, for example. The ones who sent the signal that woke you...Knowledge has its own rewards, don't you think?"
Sylens reveals something here which even Aloy doesn't yet understand. Someone -- or something -- sent the signal that freed the subordinate functions from the benevolent GAIA. Could it be the crazed Ted Faro, somehow still alive after his war company was responsible for the Faro Swarm? Did the Odyssey space program secretly succeed with malicious motives against Earth's new people? Or is it an entity we can't even begin to speculate upon? Whatever the case, HADES certainly lies at the heart of Horizon Zero Dawn's greatest mysteries, mysteries which will hopefully continue to be explored in games to come.