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"While vile mutants still draw breath, there can be no peace. While obscene heretics' hearts still beat, there can be no respite. While faithless traitors still live, there can be no forgiveness."

—Verse I of XXV of the Silver Skulls Chapter's Catechism of Hate

A mutant Chaos Cultist of Nurgle

Mutants are the millions of people across the Imperium of Man who have been deformed from the baseline Human phenotypic state by genetic mutation. This mutation can be caused from birth by environmental factors like ionising radiation acting in utero or by exposure to the raw psychic power of Chaos.

These people are destined to become the outcasts and lower classes of Imperial society. They are shunned and are often hunted down and killed as the Imperium has little tolerance for any who deviate from the divine perfection of the baseline Human form in mind or body. Mutation is actually considered a heretical crime against the Emperor of Mankind by Imperial authorities because of its connection to sympathy or worship of Chaos.

Human mutants are often terribly misshapen creatures, abominably deviating from the normal Human form. On the other hand, not all mutants are degenerate beasts; many only bear a few extraordinary traits setting them apart from the rest of Mankind. While many mutants are born mutated as a result of their ancestors' exposure to mutagens like radiation or extreme planetary environments over many generations, exposure to the psychic energies of Chaos can also lead to rampant mutation.

Because those who secretly worship the Chaos Gods as Chaos Cultists are known to be granted mutational "gifts" by their dark masters, physical mutation can be an indicator of inner spiritual corruption by Chaos. This is another reason that all mutants are considered suspect by the Imperium's authorities and are greeted as general social pariahs by almost everyone else across the Human-settled galaxy.

Navigators are also considered mutants, but may have been intentionally created through the use of genetic engineering in the distant past, during the Age of Technology to make it possible for Mankind to use the Warp-Drive effectively over long distances for interstellar travel.

Because they are absolutely vital to the Imperium's commerce and defence, they, alongside Imperial Sanctioned Psykers and certain species of Abhumans, are the only officially-tolerated form of mutants.


"We are sent to spread our glorious gifts. Those willing to accept the bountiful Gellerpox must bow before the machine and be reborn. Those that reject these great gifts shall surely die."

Vulgrar Thrice-Cursed, Twisted Lord of the Gellarpox Infected

The Chaos mutants known as Gellarpox Infected. Gellarpox Infected often gain mutations generated by the energies of Chaos that fuse their physical forms with inorganic components.

The Imperium of Man greatly fears mutation. First off, many such growths are physically alarming, causing natural revulsion in those who witness them. Beyond simpler signs of mutation are grotesqueries such as insectoid claws, tentacles or fanged maws where no mouth ought to be.

Rampant growth of meat and bone can create twelve-foot-high monstrosities whose fists are capable of bending plasteel, and whose mass can absorb bolt shells that would fell an ordinary person. There have also been many recorded instances of mutants whose flesh has melded with machinery or other inorganic technology, often through the reality-warping power of Chaos.

Yet it is not just the appearance or abilities of mutants that rankles the right-minded citizens of the Imperium, for those whose physical forms are marred by Warp energies often harbour deviant intent, spreading bloodshed and mayhem. Worse still, the most afflicted become willing pawns of the Dark Gods, foul agents of Chaos corruption actively dedicated to spreading ruin and overthrowing the Imperium.

As deadly as those physically mutated are, Humans exhibiting mental mutations are more dangerous still. Known as "psykers," these individuals can accomplish seemingly impossible things by opening their minds to the power of the Warp, such as glimpsing the future, moving objects through willpower alone or reading people's thoughts. Because of their connection to the Immaterium, psykers are more susceptible to the seductive power of Chaos, and might even unwillingly open a gateway to the Warp through which Daemons will spill into reality.

It is easy to see why Imperial citizens are trained to treat even those that carry the least of mutations without any mercy, the Imperial Creed demanding they be captured and turned over to higher authorities as part of one's divine duty to the God-Emperor.

Strangely enough, those mutations that are caught early enough and deemed to be controllable are seen by the Imperium as blessings instead of curses. Without this class of "trainable" mutants, Humanity could not hope to rule the stars. But for every sanctioned mutant that serves the Imperium -- whether as a member of the stable Abhuman divisions of the Astra Militarum, the Navigators that guide Mankind's starships through the Warp by the Astronomican's light, or even Sanctioned Psykers -- there are a thousand lesser mutants that are slain outright, and another thousand that dwell hidden in the shadows, rightfully afraid to reveal themselves.

In search of acceptance or protection, many mutants join Chaos Cults or seek out their own kind, huddling together in the catacombs and undersumps beneath Imperial metropolises or surviving in the wastelands of radiation-ravaged worlds. Some stow away or earn passage on starships bound for the fringes of the Imperium, where they can start a new life on a world untouched by the tyranny of intolerance.

With the opening of the Great Rift in the Era Indomitus, huge waves of mutative Warp storms washed over the galaxy, carrying the seeds of the Dark Gods' corruptions. Some of those seeds sprouted immediately in the form of mutation outbreaks, Zombie Plagues and worse.

Others lay dormant, as if awaiting the right moment to blossom into new horrors; indeed, many of those voidships lost in the Warp during the blackness of the Noctis Aeterna emerged having been deeply -- and often unknowingly -- changed by the Empyrean's transmutative tides.

Life in the Imperium for Mutants

Various Mutants

Ordo Hereticus pict-file displaying the menagerie of mutants encountered by the forces of the Inquisition.

On many Imperial planets, mutants are quickly abandoned by their parents and have to learn how to take care of themselves. They are almost always the worst off people in Imperial society. It is very rare to find a world that will tolerate them and not discriminate against them.

These worlds are a paradise for mutants compared to most worlds of the Imperium. Desperately seeking some form of acceptance, many mutants join rebellious cults. Most of these cults simply condemn the faults of Imperial society but others worship Chaos or xenos and plan rebellion.

These cults easily corrupt mutants due to the discrimination they have suffered. On most worlds that allow mutants to exist, usually as a form of legally discriminated underclass, they are not allowed to carry weapons for fear of rebellion. The weapons they do come to possess will often be primitive -- chains, knives, Stubbers and other simple ballistic weapons like slug-throwing revolvers.

Mutant Rebellions and Witch Cults in the Imperium

The existence of "accepted" mutant populations (where the direct touch of the Warp is not evident) has always been a two-edged sword for the Imperium's authorities. Such unfortunates are often vital to economic operations, but they represent both a problem for civil order and a ready source of rebellions, riots, and cult activity.

The history of many Human worlds is rife with such uprisings, and such conflicts are always bitter and merciless affairs. While Imperial Law and the Imperial Creed protects the Imperial citizen from the worst privations of oppression on most worlds, those not classed as fully Human enjoy no such defence from brutality and exploitation by those in power.

The situation is worsened because most "normal" Imperial citizens fear the mutant as an unclean, unnatural, and inherently tainted thing, and many mutants return this hatred with interest.

Mutants are often exiled to hellish conditions such as those in the Calixis Sector found in the deep rad mines of Sepheris Secundus or the choking fumes of Solomon's chemworks. Vilified, exploited, and outcast from the comforts of Imperial society such as they are, Abhuman and mutant populations can prove a fertile breeding ground for all manner of heretical beliefs.

Anything that offers some sliver of solace, acceptance, or the chance to strike back at their oppressors will find ready converts. The most dangerous of such outlawed and secretive sects have wyrdlings and witches at their head.

Mutants, particularly on worlds where there is a lingering Warp taint, can have a much higher inherent incidence of psyker potential than the general Human population of their given world. This problem is further exacerbated because given the mass of physical and mental distortion among their fellows, and the general antipathy among the Abhuman castes toward the authorities, it can be much easier to hide a psyker's gifts. Also, most who do not willingly succumb to the harvest of the Black Ships are forced to flee into the industrial wastes or the shadows of the underhive.

Given such a dangerous and fearful life, it is common for such rogue psykers' powers to grow should they survive, hunted and harried, their hatred for the Imperium inflamed by their ordeals. While some rogue psykers and witches revert to a solitary, almost bestial state, many mutant witch-kin gather followers about them, founding cults in their own name. On isolated Feral or Feudal Worlds, such witch cults are a source of dread, shrouded by superstition and false belief.

In the burgeoning clamour of the Imperium's heartlands, these witch–kin commonly sink to the depths, cowing dregs, abominations, and outcasts into submission with the brutal display of their powers. In rarer cases (and if the psyker is subtle and powerful enough), the most dangerous will infiltrate the hive city above.

Although often small in number and limited in scope, witch cults can prove extraordinarily dangerous if left to fester unchecked, adding power to a mutant uprising or becoming doorways to Daemonic horrors from beyond.

Imperial Hatred of Mutants

"Twisted in flesh is twisted in soul."

— Abbess Sevencia of Sisk



A mutant in combat.

The deep Imperial hatred for mutants and deviation from the standard physical Human form is rooted in the earliest days of the Horus Heresy. During the Emperor's Great Crusade in the late 30th Millennium to reunite the scattered colony worlds of Humanity under the aegis of the newborn Imperium, mutants like Beastmen were accepted and used as part of the Imperial Army, formed into their own squads or mixed with the ranks of the regular troops.

However, after the Horus Heresy, mutants were outlawed by the High Lords of Terra for the part they had played in that terrible rebellion as the favoured servants of the Dark Gods. The post-Heresy association of most mutants with heretical activities and Chaos Cults has only cemented this hatred of them by the majority of the Human population of the Imperium.

Khorne's forces have perhaps more mutants than those of any of its fellows among the major Chaos Gods, for many find it an easy path to channel their hate for Imperial prejudice into battlefeld fury. Many of their twisted mutations lend themselves to combat as well. Razor claws replace hands, muscles triple in mass, acid blood seeps from wounds, and more.

All these blessed improvements find favour with the Lord of Skulls, as all are valuable traits for the battlefeld. A mutant with such blessings and a heart full of rage is a tool Khorne can use, but even one without such useful mutations is welcome as long as the fire within the altered form burns for blood and skulls.

The Blood God offers mutants the power to exact vengeance on the minions of the Corpse God that turned their backs on them, and this power is often eagerly accepted.

Godolkin Index

In the 41st Millennium, the official document outlining the differences between Humans and mutants is the Godolkin Purebreed Guide, a treatise that describes the subject's deviation from the standard Human phenotype according to a system of points; the more severe the mutation, the higher its value in points on the Godolkin Index.

While on most Imperial worlds, a tolerance of up to 3 points is given, some worlds may be granted exemptions by the Administratum due to their strategic value or unusual and highly, mutagenic planetary environments.

For instance, on the Industrial World of Kalidar, emergent psykers are only terminated if they deviate by more than 14 points from the baseline Human genome.

Psychic Mutants

Mutant Mob

A horde of Chaos mutants in conbat.

There are many types of mutations and some affect the mind rather than the physical body, producing individuals with the ability to access the psychic energy of the Immaterium and use it to reshape the physical world. These psychic individuals always run the risk of becoming a host for the malevolent entities dubbed "Daemons" that inhabit the Warp.

These mutants are generally referred to as "psykers" in Low Gothic and they are among the most feared of Human mutants. Humanity is not a naturally psychic species like the Aeldari or the Orks and the ratio of physical to mental mutation among Humans is approximately 1000:1, or 1000 physically mutated individuals for every one born with psychic abilities.

Psykers are not left to live out their existence like most mutants but are taken from their homeworlds by the Imperium as part of the Great Tithe in the Inquisition's Black Ships to be trained by the Adeptus Astra Telepathica since they are considered far too dangerous to be allowed to exercise their abilities without proper Imperial conditioning.

The training of Sanctioned Psykers by the Imperium allows them to be used in battle with the Astra Militarum, to fuel the power of the Astronomican by sacrificing their lives to help the Emperor maintain that great telepathic beacon of interstellar travel or to serve in the choirs of astropaths who telepathically communicate between distant worlds.

They are tested for aptitude by the Adeptus Astra Telepathica and the dangerously unstable or those deemed too mentally or spiritually weak to protect their minds from Daemonic possession are executed immediately. The survivors are taken in the infamous Black Ships of the Adeptus Astra Telepathica to be transported to Terra for their training.

Some will eventually serve in the roles mentioned above or are even assigned to the service of the Astra Militarum. The luckiest psykers may be discovered by and adopted into the Chapters of the Space Marines before being handed over to the Adeptus Astra Telepathica where they become Librarians. Some may even eventually be accepted into the retinue of an Inquisitor as an Acolyte and eventual Throne Agent, if they do not eventually rise to become Inquistors themselves.

Psykers wield many and various powers, including the ability to gaze into the future, to shoot lightning out of their hands, to control the actions and minds of others and, most dangerously, to open portals from realspace into the Warp.

The Warp is inhabited by many horrible and powerful entities such as the Chaos Daemons and the Enslavers. Psykers are like lights in a dark cave to these entities who can see them when they use their power and who desire an entry into the physical universe where they can unleash great mayhem among mortals.

Therefore, whenever psykers use their powers they are at risk of possession by these Warp entities. A possessed psyker acts as a portal for Daemons into the material world and may become a horrific Daemonhost themselves, spreading the corruption of Chaos wherever they go. As more Daemons come through the portal, they tear open the gateway further, slowly pulling a portion of the physical world into the Immaterium until reality begins to warp and reform under the strain of Chaos.

Untrained psykers have no hope of survival against such an attack, and it was the occurrence of such tragedies when uncontrolled Human psykers first began to appear at the end of the Age of Technology that helped bring on the terrible destruction that consumed Human space during the Age of Strife.

Not all who are touched by Chaos sought the attention willingly. The raw stuff of Chaos permeates the fabric of reality, warping and twisting it on a whim. Inquisitors and others who deliver Imperial justice hunt down and kill mutants as part of their duty to keep the foul taint of Chaos from destroying all that their God-Emperor has built.

Even being a loyal citizen does not spare these mutated people from the purging fires of judgement. This can easily be seen as a betrayal to the mutants. With nowhere else to turn, they will seek each other out and devote themselves to the Dark Gods.

Other Races and Mutation

The powers of Chaos also produce mutation among the members of other intelligent species that are capable of being corrupted by it, but Mankind, with all of its psychic and spiritual flaws and weaknesses, has always been particularly vulnerable to the temptations of Chaos and the mutations it brings.

Among the allies of the T'au, the species known as the Kroot possesses the in-born ability to alter their own genomes and transform their physiology following the consumption of their enemies' bodies, gaining phenotypic traits that may add to their fitness as individuals and as a species.

Though whether this is true mutation or simply an atypical feature of the Kroot's natural genome is unknown to the Genetors of the Adeptus Mechanicus.


  • Black Crusade: Core Rulebook (RPG), pp. 20, 25, 50, 360
  • Black Crusade: The Tome of Blood (RPG), pg. 17
  • Dark Heresy: The Disciples of the Dark Gods (RPG), pg. 57
  • Warhammer 40,000: Rogue Trader (1st Edition), pp. 52-57
  • Warhammer 40,000: Rulebook (6th Edition), pp. 148, 158, 172-173, 177, 180, 218-219, 232, 404-405
  • Baneblade (Novel) by Guy Haley, pg. 263
  • Kill Team - Rogue Trader (Specialty Game), "A Growing Sickness"