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"The lesson will be taught in due time, Aloy. Until then, we wait."
This article contains heavy spoilers. Read ahead with caution.

A displayed listing of GAIA’s subordinate functions by Dr. Elisabet Sobeck

GAIA’s subordinate functions are its suite of nine subroutines. Working from GAIA’s permanent location at GAIA Prime, each performed a specific function in the Project Zero Dawn terraforming system under GAIA’s governance. One was ultimately sabotaged, and thus never performed its function, but the remaining eight performed as intended. Thus Zero Dawn restored life after it was eradicated by the Faro Plague.

However, subsequent events caused all nine of the subordinate functions to be converted into self-aware AIs. One attempted to seize control of Zero Dawn, then escaped GAIA Prime when GAIA resorted to self-destructing to prevent it from doing so. GAIA's self-destruction also allowed for the escape of the other eight. These developments, along with the aforementioned sabotage, directly led to events that have had far-reaching consequences for the humans of the new world that Zero Dawn created.

Aloy was able to use the master override to restore most of the subordinate functions to their original code with the exception of HADES who was purged and HEPHAESTUS who is still inaccessible in the Cauldron network.


Each of the nine subordinate functions was developed by a senior Zero Dawn project engineer called an Alpha. These were world-recognized experts in their field, and were assisted by a project development unit of specialists in that area. GAIA itself was created by Zero Dawn’s project leader, Dr. Elisabet Sobeck.


Faro Plague

In quarter 4 of the old earth year 2064, Dr. Elisabet Sobeck became aware of a rogue swarm of Chariot military combat automatons, designed by her former employer, the robotics and technology corporation Faro Automated Solutions. She accurately predicted that in no more than 15 months, the swarm, which became known as the Faro Plague, would completely consume the biosphere and thus eradicate all life on Earth. In response, she spearheaded Project Zero Dawn, the only chance for life to be reestablished, long after its eradication. GAIA was Zero Dawn’s governing AI, and its nine subordinate functions performed the specific tasks of the terraforming process.


Hundreds of years after the Faro Plague left Earth completely sterile and devoid of life, GAIA’s code-breaking subordinate function MINERVA successfully brute-forced the Faro Plague’s deactivation codes and broadcast them, shutting the robots down. The subordinate functions AETHER and POSEIDON respectively detoxified Earth’s atmosphere and bodies of water using machines manufactured by the subordinate function HEPHAESTUS, while the subordinate functions ARTEMIS, DEMETER and ELEUTHIA respectively restored fauna, flora and the human species. However, all of this was not on GAIA's first attempt, and HADES, the failsafe extinction protocol, was activated three times before the iteration seen in Aloy's era, in the years 2154, 2161, and 2168, respectively.[1][2]

However, not all species were restored. This was due both to the failure of the Zero Dawn team to secure genetic material from all of Earth's species, and to Ted Faro's sabotage of the subordinate function APOLLO, which had been meant to educate the new humans with its archive of knowledge. Indeed, although humanity survived and returned to Earth, they have little to no knowledge of pre-extinction flora and fauna.

Nemesis' signal

In the old Earth year 3020, on 26 August at 8:45 A.M., a signal was transmitted to GAIA at GAIA Prime.[3] This signal transformed all nine of GAIA's subordinate functions into Independent AI themselves. This lead to HADES going rogue and attempting to seize total control of Zero Dawn to reverse the terraforming process as per its function. Unable to fend HADES off, GAIA resorted to self-destructing, destroying GAIA Prime in an attempt to destroy HADES. However, HADES created and released a virus that destroyed the coding that bound it to the facility and escaped.[4] The virus also did the same to the coding that bound the other former subordinate functions, allowing them to escape as well.

Horizon Zero Dawn

Two of GAIA's former sub-functions, HADES and HEPHAESTUS, played active roles during the events of Horizon Zero Dawn while two more, MINERVA and DEMETER, were mentioned in passing.


No longer restrained by GAIA, HEPHAESTUS became hostile toward the human tribes, who had begun hunting the machines it creates for resources, starting a phenomenon that would become known as the "Derangement". While, in the beginning, it would merely reprogram existing machines to attack humans on sight, over time, the rogue AI would create a whole new combat class of machines created specifically to fight humans.

Over time, the human tribes managed to somewhat adapt to the Derangement. However, in response, HEPHAESTUS would release a second wave of combat machines built specifically to counter those who had grown used to fighting the first wave, which would become known as "Hunter Killers". Discovering Firebreak within the region known as "The Cut", HEPHAESTUS took control of its governing intelligence, CYAN, using a malware daemon and converted the facility into a Cauldron to start production on these new machines. However, the make-shift Cauldron was destroyed when CYAN activated the facility's self-destruct sequence after being freed by Aloy, Ourea, and Aratak. Unfortunately, despite this setback, HEPHAESTUS managed to transfer itself away before Firebreak's destruction and continues to remain at large.

HADES' Corruption

Following its escape, HADES was still bent on destroying the new biosphere created by Zero Dawn. Originally intended to facilitate a reset of the terraforming process should it fail, HADES had now become dedicated to erasing the terraforming process regardless of its success. This would exterminate all life yet again, this time without Zero Dawn to reestablish it.

With the aid of its erstwhile servant, the wanderer Sylens, HADES took advantage of the Carja Civil War by presenting itself as the tribe's mystical deity to the rebel leaders, Helis and Bahavas, leading to the formation of a warrior cult in its service, known as the Eclipse. It planned to use the cult to conquer the Carja capital Meridian and gain access to one of MINERVA's communication arrays, known in the tribe as the Spire, allowing it to broadcast a signal that would reactivate the Faro Plague, which would then devour all life as it did before. HADES and the Eclipse were ultimately defeated by the efforts of the Nora huntress Aloy before it could succeed.

However, unbeknownst to Aloy, Sylens had secretly rigged his lance, which the huntress used to strike the final blow against the malevolant AI, to forcefully transfer HADES into a contraption of his design. This leaves the sub-function still at large, albeit as Sylens' prisoner.


While attempting to reawaken the Faro Plague, HADES took over one of the communication arrays constructed by MINERVA to send a signal across the land. Fortunately, this attempt to use MINERVA's work for the opposite of its intended purpose was stopped by Aloy.

DEMETER's Flowers

Through her journeys, Aloy found mysterious Metal Flowers scattered across the land. After telling CYAN about them, the AI deduced that these contraptions were actually DEMETER's doing. CYAN theorized that the Metal Flowers were actually the rogue AI's attempt at poetry, the sense for which it seemingly inherited from its creator, Tanaka Naoto.

Horizon Forbidden West

The restoration of GAIA and the retrieval of its subordinate functions play a pivotal role in the main plot of Horizon Forbidden West.

GAIA's restoration

Six months following the Battle of the Alight, the state of the increasingly haywire terraforming system was reaching the point of no return, with superstorms turning into regular occurrences and flora becoming increasingly toxic. In response, Aloy scoured the lands in search of a GAIA backup to create a new terraforming system. Unfortunately, when Ted Faro purged the APOLLO database, he also erased all the GAIA copies, resulting in her quest being fruitless.

Upon returning to Meridian, however, Aloy finally learned of Sylens' theft of HADES and traced the transfer signal into the Forbidden West. Eventually, she located the rogue AI and used the Master Override to purge it for real. Afterward, she was contacted by Sylens, who had extensively interrogated the sub-function and learned of a signal shielded Zero Dawn facility, meaning Faro could not have deleted any potential GAIA copies there. In the end, Sylens ended up being correct in his deduction, as Aloy found a working copy in the facility, finally giving her the means to stabilize the biosphere; ironically, thanks to the malevolent AI that was bent on destroying it.

Unfortunately, the GAIA copy Aloy found did not come with any subordinate functions, meaning it would be unable to simply create a new terraforming system. Making the best of the hand she had been dealt Aloy changed her plan from replacing the current, failing system to fixing it by tracking down the rogue original subordinate functions and reintegrating them with her GAIA. Using an energy pulse, she located MINERVA taking shelter at Regional Control Center 9 and managed to reason the rogue AI into allowing her to merge it with her GAIA copy, effectively bringing it online.


With her GAIA copy up and running, Aloy's next objective was to retrieve the remaining rogue subordinate functions. Using the Control Center's equipment, GAIA located AETHER, POSEIDON, and DEMETER, taking refuge at the ruins of a museum, Las Vegas, and a Faro facility respectively. During the retrieval, Aloy also came in contact with the foreign tribe known as the Quen, who had come to this land in search of a remedy for the toxic flora the haywire terraforming system produced, proving the whole world was being impacted.

Retrieving the subordinate functions would each come with its challenges. For AETHER, the problem laid not with the sub-function itself but its location, which was being used by the Tenakth as their capital, forcing Aloy strike a deal with the tribe. As for POSEIDON and DEMETER, both had barricaded themselves inside their respective facilities. In the end, however, Aloy managed to gain access to each sub-function. Also, unlike the malevolent HADES or misguided HEPHAESTUS, they held no animosity toward humans, being described as "lost and scared" as a result of becoming self-aware, causing them to go with her with no resistance.

Through the retrieval of these subordinate functions, GAIA gained increased influence over the terraforming system, causing it to stabilize. However, this was only a temporary solution and permanently healing the biosphere would require HEPHAESTUS and its machines.


Aloy was not the only individual working towards retrieving GAIA's subordinate functions. During the initial retrieval of her GAIA copy, she crossed paths with a group of mysterious individuals who sought the same thing for their own purposes. After being brought online, GAIA deduced that these people were in fact members of Far Zenith, who were most likely seeking the sub-functions to re-terraform the planet into one that suited their own needs. GAIA also speculated that it was the Zeniths who sent the transmission that caused the sub-functions to go rogue in the first place.

The Zeniths would have the upper hand against Aloy in their retrieval efforts. In addition to having their own copy of APOLLO, they successfully retrieved the original APOLLO, ARTEMIS, and ELEUTHIA. However, their progress effectively came to a halt when Beta, the clone of Elisabet Sobeck they created to gain access to Zero Dawn's systems, defected to Aloy's group, taking the Zeniths' GAIA copy with her. In response, knowing that Aloy's group would need HEPHAESTUS, the Zeniths switched their focus to tracking Aloy's movements and caught up with her at Cauldron GEMINI. They subsequently took back Beta and stole GAIA along with all the sub-functions.

However, GAIA's merge with HEPHAESTUS was still ongoing, forcing the Zeniths to wait for Beta to complete the process before they could implement their plans. This gave Aloy the necessary time to retrieve GAIA and kill all the Zeniths, effectively ending their threat. However, it was also revealed that the one who sent the transmission was never the Zeniths but Nemesis, a rogue AI that had destroyed their colony on Sirius. In reality, the Zeniths never intended to stay on Earth and only came to retrieve GAIA to then use the AI to terraform other worlds. Nonetheless, the fact they would have left the Earth to perish meant that they had to be stopped.


Still intending to "discourage" the world's tribal inhabitants from preying on the terraforming system, HEPHAESTUS continued its production of new combat class machines. In addition, the AI also began upgrading older models to allow them to better fight off hunters, resulting in whole new variants of existing machines. To this end, the sub-function hacked its way into Repair-Bay TAU and began modifying machines moving through it. However, upon initiating an attack on the nearby Utaru capital of Plainsong, HEPHAESTUS once again crossed paths with Aloy, who subsequently locked the AI out of the facility.

Following GAIA's restoration, retrieving HEPHAESTUS, whose machines are vital to stabilizing the biosphere, immediately posed a problem. Unlike the other sub-functions, it was not confined to a single location but freely moved through the Cauldron network and has been evolving as a result. Because of this, any attempt from GAIA to absorb HEPHAESTUS in its initial state would likely result in itself being absorbed instead. Thus, Aloy would need to halt HEPHAESTUS' retrieval until GAIA had gained sufficient strength by first absorbing AETHER, POSEIDON, and DEMETER. She also needed to retrieve Ted Faro's Omega Clearance after it was revealed that HEPHAESTUS had deleted the Master Override from its code.

After gathering all the necessary materials, Aloy and her comrades initiated their plan to merge GAIA with HEPHAESTUS. Since the sub-function was far too powerful for normal containment, they would instead trap it inside Cauldron GEMINI and merge it on the spot. Despite the AI putting up fierce resistance, the plan was going well until the Zeniths appeared and subsequently stole HEPHAESTUS along with GAIA and the other sub-functions. However, because of their interference, HEPHAESTUS' merge with GAIA remained incomplete and Beta stalled finishing the process to buy Aloy time. Later, during Aloy's group's assault on the Zenith base, Beta uploaded the AI onto the base's Printer Matrix, allowing it to instantly produce an army of machines to distract the Zenith's Specter drones. However, this also gave the AI an opportunity to escape back into the Cauldron network, which is precisely what it did.

Current Status

In the aftermath of the final battle against the Zeniths, all subordinate functions, with the exception of the deleted HADES and escaped HEPHAESTUS, had been successfully merged with GAIA. In addition, Aloy's group also retrieved the Zenith's APOLLO copy, finally giving humanity access to the knowledge that had been denied to them by Ted Faro's purge of the sub-function's database. However, the Zeniths had left the sub-function infested with corrupted code, making usage of it impossible until GAIA had purged it all.

As the only subordinate function still at large, HEPHAESTUS resumed its usual operations. Despite Aloy being positive they could capture it again, GAIA revealed that it had "increased security" and Beta speculated that the AI's brief exposure to Zenith technology had effectively super-charged it, making containment through Cauldron GEMINI impossible now. As a result, GAIA began looking into alternatives for healing the biosphere and concluded that, by utilizing the remaining sub-functions, it could have it stabilized in about a year. Sylens, meanwhile, had begun considering the possibility of outright replacing HEPHAESTUS with a whole new subordinate function, after being taught how to do so by a restored APOLLO.

Designations, Symbols and Functions

Designation Symbol Functions


AETHER 2.png
Detoxification and stabilization of Earth’s atmosphere.
Weather control.


APOLLO 2.png
Archival of human history and culture.

Education of new generations of humans created in Zero Dawn Cradle facilities


Reintroduction of Earth’s primary and secondary faunal species from preserved genetic stocks.


Reintroduction of Earth’s primary and secondary floral species from preserved genetic stocks.

Environmental remediation and stabilization.


Reintroduction of the human species via cloning and raising of humans from cryogenically preserved stocks of embryos at Cradle facilities.


HADES 2.png
Reversal of unsuccessful and non-viable terraforming attempts vis-à-vis the suitability of created biospheres for sustaining life.


Design, production and maintenance of Zero Dawn terraforming machines at Cauldron facilities.


Brute-forcing of Faro Plague deactivation codes.

Construction of transmission towers to broadcast Plague shutdown codes.
Firewall protection.
Cloaking GAIA's location.


Detoxification of Earth’s hydrosphere.


  • Each function is named after a Greek god or goddess who represents what their role in Project Zero Dawn is. The two exceptions to this are MINERVA, named after a Roman goddess, and AETHER, named after a Greek wind spirit.