All of the AIs in Horizon Zero Dawn and Horizon Forbidden West, explained

In addition to a wide cast of human characters, Horizon Zero Dawn and its sequel Horizon Forbidden West are full of artificial intelligences, all of which are major players in the game’s story. In fact, there are so many of them that it can be hard to keep track. So who are these AIs and what role do they play?

Talking about all of this will require a certain amount of spoilers for the games, so be warned: this post is full of spoilers for both games, and we’re starting with the Horizon Zero Dawn spoilers right now.

These AIs were created by Elisabet Sobeck in an effort to preserve the world for future generations after automated, self-replicating war machines rampaged out of control, dooming the world and everyone in it. But even though her Earth — and all of its inhabitants — had no hope of stopping the machines, Sobeck saw hope for the future in Project Zero Dawn. This ambitious plan created AIs that would spend decades breaking through the encryption on the machines to shut them down, then terraform the world and repopulate it with cloned animals and humans. And with no one around to oversee the effort, the responsibility fell wholly to the AIs.

If you need a bigger refresher, we have a writeup on lore of the first game, as well as the biggest characters who shaped it: Ted Faro and Elisabet Sobeck. If you just want a recap of the AIs from the first game, and don’t want to know about Forbidden West, don’t read past the entry on POSEIDON. You’ve been warned.

These are all of the AIs you’ll meet in Horizon Zero Dawn and Horizon Forbidden West.

CYAN was designed to protect Yellowstone

The Caldera of Yellowstone Analytic Nexus — or CYAN — predates the creation of the Zero Dawn AIs by over two decades. CYAN was designed in the 2040’s as part of Project Firebreak, which monitored and regulated the Yellowstone supervolcano that was threatening to erupt “relatively soon,” in geological terms. CYAN operated in her role for over a thousand years, hidden from the machines in a subterranean base near the volcano. When we meet CYAN in the HZD Frozen Wilds DLC,

CYAN was a remarkably sophisticated machine mind, but was significantly outperformed by the later Zero Dawn AIs. In HZD’s Frozen Wilds DLC, we see that CYAN has been essentially enslaved by HEPHESTUS, one portion of Project Zero Dawn. (We’ll talk more about HEPHESTUS later.)

Aloy met CYAN while pursuing HADES in the Frozen Wilds expansion to Horizon Zero Dawn and freed her from HEPHESTUS’ control. As a DLC, this was something of a stand-alone story, and we may not meet CYAN again. But the rest of the game’s AIs are significant characters moving forward.

GAIA, the core of the Zero Dawn AIs

GAIA was the culmination of all of Project Zero Dawn’s hopes. Elisabet Sobeck built GAIA, a highly advanced AI that included a number of subordinate functions designed to handle specific tasks. Programming GAIA and building the Cradle and Cauldron facilities that would do the work of cloning new humans and creating terraforming machines, took place over a brief 15 months: all the time humanity had before the machines stripped the Earth of all life. GAIA was in charge of reintroducing life to our dead world, directing her subordinate functions and all of Zero Dawn’s facilities in their tasks. It took them over a thousand years, but GAIA succeeded in reintroducing life… at least to an extent.

GAIA’s job was complicated by the fact that Ted Faro, in a fit of hubris and pique, decided to delete the APOLLO database that was designed to educate future humans. Faro felt not educating future generations would leave them pure, protecting them from the horrors of technology that destroyed the world. This left GAIA unable to perform one of her primary functions, which would be preparing humans to return to the Earth and rebuild the world. While the GAIA was designed to create a new world for humanity to inhabit, humans were still supposed to do some of the work: once they were born, raised, and educated by GAIA, they should have helped run the terraforming system and repopulate the Earth with a full range of plants and animals.

Without APOLLO, humanity went out knowing nothing, and in Zero Dawn and Forbidden West, they live in scattered tribal societies, with little technology. The Earth as we see it in the Horizon series lacks many of the animals that were intended to be reintroduced by humans, rather than by the machines controlled by GAIA. Humanity survived the machines, but lacks many of the benefits Sobeck had planned on them having.

There was another snag, too: in the year 3020 when a signal of unknown origin caused GAIA’s subordinate functions to become full AIs, no longer subject to GAIA’s oversight. The newly-sentient AIs ran rampant without the guidance of a central intelligence, and GAIA chose to self destruct in an attempt to destroy HADES — the most destructive of the AIs.

It stopped HADES for a time, but now all the AIs were free… and without backups or anyone who might be able to use them, GAIA seemed to be gone for good.

GAIA’s subordinate functions, now all full AIs

We’ve seen — and even interacted with — some of GAIA’s subordinate functions throughout the Horizon games, but some exist in name only. Remember, if you don’t major spoilers for Forbidden West, stop reading after the POISIDAN entry.

AETHER

AETHER was designed to detoxify the atmosphere of the planet, which had been left choked with pollutants by the global war with the machines. We don’t know exactly how successful AETHER was, but the presence of breathable air on Earth in Horizon indicates that it managed to do at least some of its work.

AETHER does not appear in Horizon Zero Dawn.

APOLLO

APOLLO was designed to re-educate humanity, but after Ted Faro deleted its database of knowledge, there was no way for it to complete its task. It’s unclear whether APOLLO still exists or became a full AI when the mysterious signal released all of GAIA’s subordinate functions.

But regardless of whether APOLLO is somewhere in the world of Horizon, he remained offline when he should have been teaching humanity how to survive. This meant that neither ARTEMIS or ELUTHERIA could fully complete their tasks, and modern humans exist at more of a late bronze/early iron age level of technology.

We know that an early version of APOLLO — including the database — was traded to the Far Zenith project, which was an attempt to save humanity by colonizing distant stars. In exchange, Zero Dawn got some of the cloning technology needed for ELUTHERIA.

APOLLO does not appear in Horizon Zero Dawn, though his absence casts a long shadow over the game’s events.

ARTEMIS

ARTEMIS was designed to reintroduce animal life and shepherd humanity to be responsible stewards of the new biosphere. But without APOLLO, humanity never received the proper education to help ARTEMIS. Still, ARTEMIS did manage to introduce enough life to make Earth livable again, though many species of animals appear to be missing from Horizon.

ARTEMIS does not appear in Horizon Zero Dawn.

DEMETER

DEMETER was designed to reintroduce plant life, and it’s fair to say it may have been the most successful of the subordinate functions, because the diversity of plant life on Earth in the 31st Century is impressive. We haven’t met DEMETER, but there are tantalizing clues in the metal flowers seen throughout HZD and HFW that suggest she may continue to fulfill her original purpose… though she may also play a role in the slow corruption of the world following GAIA’s death.

DEMETER does not appear in Horizon Zero Dawn.

ELUTHERIA

ELUTHERIA was designed to essentially resurrect humanity, using cloning technology and a vast array of gestation mechanisms to create the first generation of future humans. But without APOLLO, ELUTHERIA couldn’t educate her charges past a kindergarten level, and was forced to release them out onto the world to fend for themselves. All modern humans in Horizon are the descendants of these first cloned humans.

ELUTHERIA does not appear in Horizon Zero Dawn, though Aloy returns to one of her cloning facilities hidden under All-Mother Mountain.

HADES

HADES was designed to “reset” the world if the terraforming system failed to create a viable biosphere, and this destructive AI was the principal antagonist of Horizon Zero Dawn. Since GAIA was compassionate by nature, it would be exceedingly difficult for her to give up on a failed attempt to restore the biosphere, which would waste limited resources trying to preserve an Earth that could never support life.

So the HADES subordinate function was a necessary evil that would take control of the terraforming network, destroying the unviable biosphere to reduce the Earth to a blank slate so GAIA could start again. In essence, HADES was a pre-programmed extinction event which would purge a doomed biome.

When the mysterious signal freed HADES, he immediately attempted to seize control of the terraforming network and fulfill his assigned task: destroying the entire biome, and all life on Earth with it. GAIA’s death stopped HADES’ attempt, but didn’t destroy him, and he spent decades working to revive and take over the original machines to destroy the Earth again.

That leads into the story of Horizon Zero Dawn, in which Aloy eventually defeats HADES.

HEPHAESTUS

HEPHAESTUS was designed to build the machines that would terraform the world, running the vast manufacturing facilities Zero Dawn had build. He’s the main antagonist of HZD’s Frozen Wilds DLC, this rogue AI

Due to the whimsy of his creator, HEPHAESTUS generally designs these robots as animals of various kinds, from giant short-faced bears to massive dinosaurs. While GAIA was in control, these robots were peaceful, even when humans hunted and destroyed them for parts and useful technology — but HEPHAESTUS views humanity as a threat to his creations and once free, he began designing fierce machines that would attack humans on sight.

As we mentioned earlier, HEPHAESTUS enslaved CYAN to use her facilities at Yellowstone to build more machines — but even though Aloy freed CYAN, he remains a significant threat to humanity.

MINERVA

MINERVA was designed to spend hundreds of years working to breach the encryption of the machines and shut them down. Once the encryption was broken, she used enormous communication towers — the Spire in Meridian is one of them — to beam the shutdown command across the world.

It’s clear MINERVA succeeded, but there’s no evidence of her activity in Horizon Zero Dawn.

POSEIDON

POSEIDON was designed to detoxify the water, much like AETHER was to detoxify the air. Like AETHER, he seems to have been successful. We do not see POSEIDON in Horizon Zero Dawn.

Those are all of GAIA’s subordinate functions, now all full-fledged AIs acting on their own in the world of Horizon.

Horizon Forbidden West has its own AIs, too

Some of HZD’s AIs play a role in Forbidden West, including HADES, GAIA, MINERVA, POSEIDON, AETHER, DEMETER, and HEPHAESTUS. But there’s one AI of note that’s brand new, and whose existence is crucial to the plot of Horizon Forbidden West.

Nemesis

The Nemesis AI was not created by the people of Earth at all, but by the descendants of Far Zenith, who left Earth to colonize a world in the Sirius system. Using the advanced technology they retained from APOLLO, they built a society with advanced medical technology that allowed them to live indefinitely. But they were unsatisfied, and worked on technology to convert their minds in a digital format so they could transfer their minds body to body, or even into machine bodies, becoming truly immortal.

Nemesis was a failed attempt at this kind of transfer, resulting in a strange AI consisting of the minds, memories, and emotions of thousands of Far Zenith citizens. They attempted to keep it locked away, but as Nemesis grew to loathe its makers, it seized control of the colony’s infrastructure, and used it to build machines to slaughter them.

When some attempted to escape back to Earth, Nemesis sent a signal to the GAIA facility attempting to transform HADES into a true AI like itself that — transforming the other subordinate functions was an accident. Nemesis assumed HADES would wipe out all life, so the Far Zenith survivors would arrive on  a lifeless rock, dooming them death.

Nemesis would have been successful if not for Aloy stopping HADES, but Nemesis didn’t give up. When it realized HADES’ failed, it built itself a ship to chase its makers, leading us to the events of Horizon Forbidden West.

And those are all of the AIs you’ll find in Horizon — the ones you meet and the ones you never see. Hopefully we’ve helped you sort them out, so you can better understand what’s going on in Horizon Forbidden West.