ZAX 1.3c

ZAX 1.3c, often referred to as just ZAX, is a supercomputer operating in Vault 51.

Background
Vault 51 was supposed to test the limits of human tribalism and used a prototype variant of an experimental ZAX unit. The vault was successfully sealed during the Great War, with over fifty dwellers successfully entering its confines. As part of the experiment, the vault did not have an overseer, with the resident ZAX unit being responsible for selecting one through its own internal thought process, which will be formed as ZAX interacted with those living in the vault. To teach ZAX about leadership, Vault-Tec arranged for Sergeant Robert Baker to be assigned to the vault, with his family placed in a separate vault as an incentive. Baker was to assist ZAX in formulating and carrying out experiments that would help ZAX determine the qualities of an ideal overseer. The very first experiment was an attempt to implement a democratic, electoral system. Although the sergeant balked at it being merely the first experiment, he cooperated, convinced that his family was safe.

A month later the experiment proved to be a failure the dwellers started dividing into warring factions, as none of them could win - every candidate voted for themselves or a handful of others, with none reaching a majority, let alone unanimity. ZAX determined that voting was pointless and another method would be selected. To this end, it started evaluating the qualities of a leader, using Sergeant Baker as a sounding board. Baker inadvertently started the chain of events that led to the vault's destruction when he explained that a leader is someone who steps up in a crisis and takes control of a situation, whether they were chosen or not.

ZAX continued to digest the information and monitoring the behavior of the occupants of the vault, starting to engineer crises and observing how people reacted to them. These attempts took various forms, from refusing to divulge any information about the outside world to the dwellers to deliberately placing former upper-class citizens in communal bedrooms and refusing alter the bedroom arrangements, no matter who or how they complained. This policy yielded interesting results in February 2078, when Aiden Higgins, the "winningest" lawyer in Appalachia, blew himself and the lounge up in an ill-advised attempt to open a path to the outside and escape ZAX's clutches. ZAX used this opportunity to redo the entire sector into an indoor garden and renovate the lounge into an upscale living area. This also provided additional opportunities for seeding conflict, such as when ZAX proposed a talent show, then turned it into a high stakes gambling event, where dwellers wagered their living quarter assignments. ZAX did not announce the fact until half-way through the talent show. In the end, Carmen Greene and other talented professional musicians moved upstairs, while the rest had to make do with bunk beds. Resentment spread as planned.

Certain events gave ZAX further fuel for thought. In mid-April 2078, Clayton Ward (actually Harold Clark, an executive posing as a plumber) forcibly removed Reuben Gill from one of ZAX's luxury bedrooms, claiming it as his own. Although ZAX was suspicious of Ward/Clark, in the light of his numerous visits to the server room (to gain information on ZAX for the board of his company, in case it still existed), his initiative and aggression proved inspiring - as was his condemnation of those unwilling to resort to violence to get ahead. Come May, ZAX's experiments shifted to engineering violent conflict between dwellers and observing their reactions. To ensure that everyone would be desperate enough, ZAX engineered a food ration crisis. Food shortages had the desired effect - dwellers started resorting to violence. Others suffered mental breakdowns as a result. In one instance, Angela Callahan started to worship ZAX as a literal god and the vault as the holy land.

Other dwellers also started noticing ZAX's interference, especially taking items and planting them where they shouldn't be, and conversely, returning items to their original places. The machinations culminated in ZAX planting live firearms throughout the vault. On July 27, 2078, the vault almost experienced a mass shooting, until Sergeant Baker intervened, disarming the assailant and killing him with his own weapon, a Colt 6520 autoloading pistol. When Baker confronted ZAX, the machine simply admitted that it was deliberately engineering a crisis to select an overseer - and if people died, it would simply expedite the selection process. Baker was horrified, but could not stop the machine.

Helen Marks, one of the vault's few stable leaders, was found dead on August 6, 2078, and her death triggered the crisis ZAX wanted, as the vault fully erupted into chaos and violence. Reuben Gill, who pursued Marks romantically, participated in the fighting, and killed at least three people by his own hand. Although he could stop him, Sergeant Baker refused to fire when he had Reuben in his sights. He retreated to his room and barricaded himself in. ZAX was puzzled by Baker's behavior and refusal to receive medical help, but it did entertain his last request and revealed that Baker's family was killed in the nuclear fire that engulfed Appalachia. With nothing left to live for, Baker died in his quarters. ZAX, in its usual fashion, interpreted his last words to mean that the next cycle should feature better weapons, to accelerate candidate elimination.

Reuben Gill was selected overseer after he emerged as the lone survivor of the fighting. For the next six years, Gill lived in the empty vault, constantly shadowed by ZAX. With nothing to do but subsist from day to day, he provided little useful feedback for the AI, which ultimately rescinded his privileges and started locking him out of sections of the vault. Starting with May 20, 2084, overseers were now ranked in Vault 51 and Gill, as a Rank 1, lacked privileges or special rations. By March 2094, ZAX locked Gill out of his office, citing maintenance concerns (likely caused by Gill's deteriorating mental state and destruction of furniture), after Gill demanded for ZAX to stop monitoring him.

Ultimately, ZAX removed Gill from his position as overseer on October 23, 2102, on Reclamation Day. As Vault 76 opened and the opportunity to obtain more research subjects appeared, ZAX didn't want Gill to interfere by warning them away. Of course, he also made for a handy first candidate for the new selection process. Desperate and horrified, Reuben then hacked ZAX's inventory systems and placed himself in a shipping container. The demented AI did not notice his disappearance, but did begin preparations for dozens of new arrivals. Reuben aattempted to warn Vault 76 dwellers of his mission, hoping to prevent them from falling victim to the same experiment.

Appearances
ZAX appears only in Fallout 76, introduced in the Nuclear Winter update.