Purifiers: protoss minds inside machines

The Purifiers were an ancient robotic race created by the protoss. Built under the direct order of the Conclave from the recorded consciousnesses of the greatest warriors in protoss history, they were intended as the ultimate fighting force, but were treated as slaves and rebelled before being banned and powered down. Long afterward they were reactivated by Hierarch Artanis to aid in the war against Amon, and afterward took their place among the Daelaam as equals. (StarCraft II: Legacy of the Void)

Nature#

The original Purifiers bore the same general protoss form, if not biology. They operated more efficiently in close proximity to one another, and a Purifier's personality could be uploaded into an empty shell. They were connected through a data web similar to the Khala, though it lacked the same emotional connectivity. Through this link, a Purifier could speak through another Purifier's body when the link was shared. Talandar, the only Purifier of the revived program, bore similar synthetic properties to the originals but took a quadrupedal form. (StarCraft II: Legacy of the Void)

Origins and rebellion#

The Purifiers were built under the direct order of the Conclave to be an ultimate fighting force, at a time when protoss scientists were advancing intelligent robotics and artificial intelligence. The program was kept in shadow and unified by the belief that consciousness could be turned into data, preserving the thought process and decision-making of a formerly living being. The Conclave moved to build a force replicated from the greatest warriors in protoss history. A data web was designed to give the Purifiers a synthetic equivalent of the Khala, which Artanis later speculated the engineers added in the belief that the Purifiers could never be seen as protoss without the light of the Khala. (Protoss Faction Lore; StarCraft II: Legacy of the Void)

The Conclave did not treat the Purifiers with the respect afforded regular Templar, regarding them as little more than slaves. Eventually the Purifiers rebelled and killed their masters. In return, the Conclave deemed them too dangerous, banned them, and powered them down, launching them away in the command vessel Cybros to be reactivated only in the direst of circumstances. (Protoss Faction Lore; StarCraft II: Legacy of the Void)

The second program and reactivation#

Sometime before the Great War, a new Purifier Program was designed, inspired by the original attempt, at a facility on Glacius. The personality of Praetor Fenix, who had fallen at Antioch during the zerg invasion of Aiur, was used as the template for the prototype, with the replication estimated to be accurate within the ninety-ninth percentile. (StarCraft II: Legacy of the Void)

During the war between Amon and the Daelaam, Hierarch Artanis came to Cybros to reactivate the Purifiers while also contending with a zerg presence there. Once activated, the Purifiers purged the zerg-infested world of Endion through the vessel's weaponry, then agreed to fight for the Daelaam after Artanis assured them they would be treated as equals, on the condition that the Purifier bearing Fenix's consciousness, Talandar, became their representative. (StarCraft II: Legacy of the Void)

Against Amon and among the Daelaam#

The Purifiers fought during the Daelaam's second attempt to reclaim Aiur, alongside the Tal'darim and Nerazim. When Amon's host body was exposed, Cybros and the assembled Daelaam fleet unleashed an open bombardment that destroyed his physical form. The Purifiers held the southern entrance of the temple during the final defense of the Keystone, commanded by Phase-smith Karax, and helped activate the Keystone to drive Amon back into the Void. When Artanis led the protoss into the Void for a final strike, Purifier sentinels, colossi, and energizers accompanied his forces. (StarCraft II: Legacy of the Void)

After the End War, the Purifiers continued to research and develop new technologies and improve their shells, repurposing many abandoned protoss technologies, much of this work done out of Cybros. On Aiur they largely kept to their own network, separate from the rest of the Daelaam except when needed for reconstruction, and were often met with distrust by their biological protoss kin. (StarCraft II: Legacy of the Void; One People, One Purpose)