The Purifiers were originally disciples of Reverend William Stryker, whose agenda is based on an extreme version of Christian fundamentalism. Stryker and his Purifiers believed mutants to be an abomination against God, and a manifestation of the Devil's evil influence on the world.
Under Stryker's leadership, the Purifiers were successful enough to capture Professor X during an attack on the X-Men which also resulted in the deaths of several mutant children. This forced the X-Men to unite with their chief adversary, Magneto, in an effort to defend themselves and free their mentor. In the end, Stryker was shot and arrested by authorities. Afterwards, the Purifiers disbanded for a time.
Eventually, William Stryker was released from prison. While out he discovered the whereabouts of the futuristic Sentinel called Nimrod. Stryker used Nimrod in order to witness the affects of M-Day months before it actually happened. Using knowledge of the future gained from the Sentinel's memory system Stryker also saved several human lives, and suggested those incidences were "miracles". This enabled him to re-energize support for the Purifiers, and he recruited many new members.
In the wake of M-Day, and the decimation of the mutant population, Stryker and his forces engaged in brutal attacks on the remaining mutants. Their belief was that God did his part on M-Day, and that it was their job to finish his work by killing the rest. Among their victims were junior X-Men, Wallflower and Icarus, the former of which was killed by Matthew Risman. Matthew would eventually become the new leader of the Purifiers after Stryker himself was killed by Elixir of the New X-Men.
Matthew Risman's Purifiers are currently one of three groups engaged in a race against time to find the Baby Mutant born since M-Day. The other two are Mr. Sinister's Marauders, and the X-Men. Each group has its own agenda regarding the child. Also, since losing his powers, Rictor of X-Factor Investigation's is now a member of the Purifiers, but secretly spying on them for the X-Men.
They are now the primary targets of the newly formed X-Force. they recently took hold of one of its members, Wolfsbane. When the X-Force took her back, they didn't know that they gave some mind-control where Wolfsbane attack Angel and ripped out his wings. Wolfsbane gave them to Risman, in turn, he extracted the technorganic strain from Angel's wings when he used to be Apocalypse's Horseman of Death. Risman use the strain to make an army of "angels" called the Choir, that will eradicate the remaining mutants.