HADES
Tasked with the unenviable duty of destroying the Earth when the efforts of GAIA and the other Subordinate Functions proved to be too far off-track, HADES was the ultimate contingency plan. It was released 20 years ago along with the rest, and lay dormant in an ancient FARO war machine until discovered by Sylens. HADES and Sylens traded knowledge, eventually partnering to build The Eclipse from the ashes of the Carja Civil War. Transitioning power to Helis, HADES tempted the Eclipse with the power of ancient war machines to retake their homeland and throne.
HADES was ultimately defeated by Aloy at the Battle of the Spire at Meridian. She was able to override the Spire to send the deactivation codes to the war machines, also driving HADES from the module in which it had sought refuge. At least some part of HADES was then collected in a containment vessel by Sylens.
Corruption
Whether or not HADES is responsible for all occurances of Corruption is not definitively explained in HZD. Corruptor machines, originally FARO Scarabs, pre-date HADES, and have always had the ability to turn other machines to their command. This effect was shown explicitly in HZD with Corruptors taking over a number of other machines.
However, the effects of the Derangement cannot be discounted — had Corruption not been seen before then? Or had it been seen in very limited cases, where some delve unearthed and reactivated a Corruptor, only to quickly be put down? Could the Corrupted Zones be places where the Eclipse had extracted and activated a Corruptor? Most of them did not show evidence of being a dig, so this is unlikely, but possible. Or are the Corrupted Zones evidence of buried Corruptors at that location, with something causing their Corruption effects to activate and take over machines in the area?
It’s also worth noting that at the Battle of the Spire, HADES is wreathed in the same flowing red Corruption effect as corrupted machines. This might then imply that HADES has the same control over Corruption that Corruptors do. A more optimistic interpretation might be that the HADES AI itself had become corrupted, indicating at least a chance of purging that Corruption and returning HADES to a “normal” state.
Plan B?
While HADES showed adaptability in its assumption of the Buried Shadow identity, and the effort to unearth the FARO war machines to carve a way to the Spire, that plan raises an interesting question: was activating the war machines the original plan conceived by the Alphas at Project Zero Dawn? If not, what was? Is there some other infrastructure for some other plan, waiting dormant somewhere, just in case HADES needed it?
HADES’ reliance on the war machines is interesting — it could be why GAIA and HEPHAESTUS don’t bother to strip dormant war machines for parts, even before the Derangement. As it seems likely GAIA would want to begin disarming and destroying the war machines to make the planet more safe for the humans, the lack of efforts to do so point to some kind of prohibition. If GAIA and HEPHAESTUS had been informed that the machines might be needed, they would know to avoid them, and instead get materials from other places.
HADES in Skyline
Skyline makes one small tweak from Horizon lore to the origin of HADES and the other Subordinate Functions. In the explanation of the events that unshackled the AIs, GAIA makes the assumption that HADES created and released the virus that set everything free. Skyline thinks GAIA was in error, letting motions cloud better judgment. GAIA saw all the Subordinate Functions break free, and assumed it was the responsibility of the one Subordinate Function GAIA could not control. Skyline lore asserts that the virus came with the disruptive signal and set HADES free, but was not created by HADES itself.
Skyline does not otherwise modify the canon HADES lore from Horizon.