The Purifiers came to be during the Rise of the Sleepers of Avarrach.
As the Sleepers poured through the rifts, the leader of the Flame Dawn, Aberion, recognized their imminent threat. The Sleeper menace would not die easily, and when one died, it would take his soldiers with it then all of them would resurrect under the influence of the virus. He tasked his Field Commander, Bromich, with finding a way to combat the ugly threat and vowed to give him whatever resources he needed. Bromich, in turn, turned his protegee, a soldier of the Flame Dawn who had shown amazing promise and had been rising steadily through the ranks: Kali.
Kali came from a magic-using nation on Talich which had been conquered by the Flame Dawn in the years before the Infinity Wars began. She had joined the Flame Dawn military when given the option and had found great success with the ability to set her blades on fire. Bromich assigned her to lead the new division, which was given the name "The Purifiers." Their goal was simple: eliminate the sleeper threat once and for all.
As the Infestation wore on, with a never-ending horde of sleepers still pouring forth from the rifts along with the now infected bodies of those they had already conquered, Kali set her plan in motion.
The Purifiers began to implement fire where they could, burning the bodies of all the dead to slow the resurrection and infection of Flame Dawn soldiers by the Sleepers. Even with all their efforts, the Purifiers could see they were fighting a losing battle. The Sleepers' numbers were overwhelming and relentlessly forced back the combined forces of the Flame Dawn, Genesis Industries, and the Warpath.
It is unclear what happened to the Purifiers following the arrival of the Overseers and their alliance with the Flame Dawn.