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Hephaestus is a secondary antagonist in Horizon Zero Dawn.


Hephaestus is a rogue Artificial Intelligence. He is never seen in-game, though it can be assumed he bears a similarity to his sibling AI Hades.


Long before the events of Horizon Zero Dawn, humanity faced its own crisis when the latest line of military robots, designed to be self-sufficient, malfunctioned and went rogue, attacking cities, self-replicating faster than they could be killed, and converting whole ecosystems into fuel. In a last ditch attempt to save life, a project known as Zero Dawn was created. Zero Dawn would be headed by a super AI and nine subordinate functions that would shut down the rogue machines, terraform the earth, and reintroduce life and humanity to the recreated world. Hephaestus was among the nine subordinate functions used by the central AI, Gaia. His role was to act as both the forge and blueprint, aiding Gaia in creating new, peaceful terraforming robots.

Although Apollo, the subfunction designed to educate the new wave of humanity about the history and knowledge of the old ones, was erased shortly before launch, Zero Dawn and Gaia succeeded in their other tasks. That is, until the Gaia Prime facility received an unknown signal, which caused all nine of the subfunctions to become true AIs that behaved erratically. Hades, the subfunction designed to reset operations to square one if things did not go as planned, attempted to take control, but Gaia responded by self-destructing, in an attempt to wipe out all of them. However, Hades launched a virus that released the subordinates from the facility, allowing them to escape to various parts of the world.

The Culling

Hades eventually landed in the core of a derelict war machine destroyed by humans during the apocalypse, trapped there for almost two decades, and alleviating the immediate threat to life. However, humanity was not safe yet. Hephaestus's new habitation is unknown, but he quickly gained access to the cauldrons, the underground factories where Gaia's robots were made. Hephaestus resented humanity for hunting the terraforming robots for their parts. As such, he took control of the cauldrons and made changes to the machines in order to cull humans. To humans, this event was known as the Derangement. Machines that were normally skittish began attacking on sight. Old terraforming machine models were given weapon modifications. And entirely new machines built for combat began appearing in the following years, claiming many lives in the process.


While the protagonist, Aloy, is constantly doing battle with the machines under Hephaestus' control, like all other humans, she would not learn of it or it's influence until she has infiltrated several cauldrons and overridden their cores, revealing logs that describe the rogue AI's intrusions and commands. If she does this early on, she initially has no idea who or what Hephaestus is, just like Hades. However, delving into numerous ruins and learning of the past reveals just what Hephaestus truly is.

The AI is still currently active somewhere, continuing to order the creation of dangerous machines.


  • Virtual Creativity: Hephaestus was designed to create any technology necessary for running and maintaining the terraforming system. Rather than limit Gaia to 21st-century designs, Hephaestus was programmed to be capable of learning and developing creative solutions to problems.
  • Vocal Communication: Hephaestus is capable of speech, albeit in a highly artificial-sounding voice. Unlike Hades, Hephaestus's speech appears to be nothing more than the diction of its processes, and never communicates with humans.