When the Great War annihilated civilization, the survivors lost their loved ones, their homes, and their worldly goods. They endured a daily search for food, water and medicine, but they also had to seek out their lost identities. People have always defined themselves by the work they do, the place they live, the things they own. In the Great War it wasn't just buildings that were destroyed - entire cultures were erased from history. In the brutal years that followed, the survivors had to define themselves again, find meaning in their existence, or face a metaphorical loss of their humanity. But a much more literal threat to their humanity was already in place, waiting quietly beneath the desert for someone to stumble across it. Someone did, nearly a century after the war, and that threat came closer to extinguishing humanity than all the bombs and guns of the old wars.
A single neutron passing through a strand of DNA can cause a cancerous tumor, but a lifetime of exposure to unprecedented amounts of atomic fallout will have wildly unpredictable results. After a few generations of passing on this defective DNA a species will begin to mutate. That explains many of the strange beasts running around the wasteland. But not all of them.
There's a different strain of mutant out there. They're shaped like men, but... bigger. Some of them are more dangerous than deathclaws, stronger than a man in power armor. They call themselves "Super Mutants" and they're not the result of random contact with radiation, but rather a deliberate act of genetic tampering.
In the years leading up to the Great War the most powerful nations became desperate for ways to outmatch their foes. Deadlier guns and ruthless propaganda created armies of fanatical solders. Still, no matter how well conditioned or well armed a soldier is, they are still only human. But that can change.
Holotapes unearthed in pre-war military installations show that the United States government started out with good intentions. Rival nations had attacked America with biological weapons, resulting in a "New Plague" so America's leaders created their own defensive virus. The plan - originally - was to make a germ that would mutate America's population just enough that they would become immune to the viruses that the enemy might use.
It was an idea so outlandishly daring that it seemed worth the risk to a government that faced imminent destruction. It could force the population to instantly evolve to a point where they were naturally immune to the New Plague - whether they wanted to or not.
In a sense this Forced Evolutionary Virus worked, but the effects were much more drastic than anticipated. The animal test subjects mutated by it were not only resistant to common biological weapons, they also grew stronger and more intelligent, but monstrously deformed.
In those last days of patriotic fervor there would have been plenty of soldiers willing to become human guinea pigs to test the Forced Evolutionary Virus or FEV. Lucky for them the war ended before the government started asking for volunteers. Huge vats of the virus were secured away in facilities on both sides of the country.
In Maryland the virus was placed in a Vault-tec Vault, and used as part of their cruel experiments. According to files recovered from a Vault-tec mainframe, the people who took shelter in that vault were exposed to the virus by their own Overseer, the very man assigned to protect them after the bombs fell. After escaping the war, these people suffered even worse than those trapped on the surface.
The mutation process is painful, and most people exposed to the virus die a horrible death in a body they don't even recognize as their own. Those who do survive often wish they hadn't, because their very humanity is taken from them. Whatever they looked like before mutating, they transform into an enormous, bald, green brute. Back then lots of people defined themselves by skin color. After mutating they were all just varying shades of green. Women lost any shred of their original gender and became indistinguishable from the male mutants. And the men? Some of them even lost the very thing that made them men.
That sudden loss of identity would enrage almost anyone. Maybe with enough therapy a person could come to terms with their new body, but most of the poor creatures suffered from another side effect - reduced cognitive capability.
Despite the virus' potential to increase intelligence in some people, most of the super mutants on the East Coast were just plain stupid.
In fact, many of their brains were too small to perform even basic autonomic functions like breathing. let alone engage in the sort of philosophical introspection that would make them at peace with themselves and the world around them.
For those that survived, there were some positive trade offs. Their strength increased tremendously, as did their size. Even the "small" ones are nearly ten feet tall. In the Capital Wasteland these beasts continue growing throughout their existence. Wanderers have reported fighting super mutants that are fifteen feet tall, and foolhardy adventures have pumped hundreds of bullets from assault rifles into mutant overlords without bringing them down.
Scouts from the Brotherhood of Steel even claim to have fought super mutants that are twenty feet tall and can survive a direct hit from a mini nuke.
Fortunately it takes a long time for a super mutant to grow to that size. Unfortunately, super mutants can live indefinitely unless they meet a violent death, and if the Capital Wasteland subspecies of mutant is not exterminated they will continue to grow in size and power.
The only factor that keeps them in check is that they are infertile and cannot reproduce - at least not the way that they did when they were still human. The first mutants created in that horrid vault might not have been as intelligent as the humans who created them, but they had strength and righteous fury on their side.
The mutants turned on their creators and transformed them into the next generation of super mutants, and in time the vault was nothing but mutants, alone, undying and just intelligent enough to know that they had been betrayed by humanity.
Forcibly stripped of their humanity, robbed of their ability to reason, and transformed into massive brutes they were an angry hoard trapped inside a vault. Rage and boredom are an unstable mixture and eventually that vault burst.
Hundreds of super mutants emerged into a wasteland where their enhanced physical abilities made them better suited to survive than the humans around them. The disorganized humans had only one advantage, and that was their numerical superiority.
Out-numbered and unable to breed, the mutants were still cunning enough to understand that they had to boost their ranks by kidnapping humans and exposing them to the virus.
Further West, things were more complicated. California and the West Coast had their share of trouble with super mutants, but those mutants... they didn't just suddenly pop out of a vault and rampage like mindless savages. The mutants of the wasteland's core region were the result of a misguided plan to set the world right.
The stockpile of FEV in Maryland was only a fraction of what the government had produced before the war. In a secret base in Mariposa California they hid vats of the virus and conducted experiments in the final months before the war.
Mariposa... Spanish for "butterfly". Maybe putting the base there was someone's idea of a joke. Humans could be dipped in the virus and metamorphosize like beautiful butterflies emerging from their cocoons. Of course, what emerged from these vats were hideous killing machines. These were just as strong and ugly as their Eastern cousins, but they were a bit smarter. Smart enough to have a plan to annihilate humanity and rule the world.
Mutated creatures weren't uncommon, so the first hints of a new threat went unnoticed. They worked with a network of un-mutated humans who masqueraded as a new religion. These Children of the Cathedral seemed like a benevolent group or at least just another harmless cult, but they were serving as scouts for the mysterious mind behind the mutant army.
The mutant army was smart enough to scour the lands for new humans to mutate, and to select people with little exposure to radiation. Using humans with DNA undamaged by radioactivity meant they were more likely to keep their intelligence after mutating. The size and capability of this inhuman swarm grew, always hungering for the purest human DNA to serve as the building blocks of a master race.
This was before the New California Republic had solidified. Before the Enclave chose to reveal itself. Back when the Brotherhood of Steel kept their technology closely guarded. There was nothing to stand against an army with such organization. Such single-mindedness.
Such... unity.
Who they had been before no longer mattered. The super mutants weren't divided by old world notions of race; and they did not bicker over religious beliefs, for they all worshiped the same Dark God, and claimed that they could hear his voice in their heads.
Did this dark god exist? Were the mutants led by some cunning mutant general? Could the master race have a Master of its own? Someone or some thing was certainly behind this new Unity movement.
A few of the older and more civilized super mutants can be coaxed into discussing their former master and what they called Unity. Further information was unearthed by the Enclave at the ruins of the Mariposa base, and the Brotherhood of Steel scribes have some additional records regarding a secret Vault-tec facility that may have been involved with the mutant army.
All of these sources agree that the super mutant army did have a leader endowed with... unique mutations, no doubt acquired after prolonged exposure to the Forced Evolutionary Virus. This creature presumably originated at the Mariposa base where it remained concealed while perfecting the process of using the Forced Evolutionary Virus.
No doubt through much trial and error, this "Dark God" created generations of flawed beasts before finally discovering that the FEV works most effectively on people who have low levels of radiation exposure. Access to pre-war computers revealed that the wasteland held secret communities of uncontaminated vault dwellers whose gene pools had been protected for generations deep beneath the earth where the radioactive fallout couldn't reach them.
It's ironic that the super mutant master was done in by the actions of one of these vault dwellers. Fearing an attack from the mutants, one of the vault Overseerers sent out a brave adventurer to stop the unseen leader of the mutants. Records are contradictory on just how the vault dweller did it. Was it with brute force? Trickery? Or maybe the vault dweller uncovered saw some pivotal flaw in the Master's plan. Maybe the unified super mutant utopia was doomed to failure all along, and the genetic engineer was "hoist with his own petard".
Regardless of how it happened, with their master gone, the mutant army scattered. The most intelligent of the Lieutenants gathered the lesser mutants into smaller bands. But without the resources and abilities of their master, these groups do not pose a threat to humanity as a whole.
The former elite guard of the mutant army have taken the fall of their master the hardest, and have become an unpredictable menace. These Nightkin as they call themselves were once the best of their species; augmenting their strength and cunning with pre-war stealth technology. They are usually still in possession of the rare Stealth Boy devices and use them without concern for the harmful effects of prolonged exposure. After decades of constant use, their minds have degenerated and their skin has darkened to a distinctive grey. They are plagued by hallucinations and imaginary friends; often their jabbering is the only sign that one is nearby. Due their tendency to appear in unexpected places and engage in bizarre behavior a single Nightkin can be more dangerous than a group of their green-skinned brethren.
Some super mutants have formed their own communities, following charismatic leaders across the wasteland. Turn a radio to the right frequency in the right parts of Nevada and there's a broadcast coming from a mutant girl who thinks she can take the Master's place and guide the mutants to a new utopia. Although she has gathered many followers, her mental instability ensures that this is... unlikely.
Other mutants simply wish to be left alone. They have searched the wasteland for remote pre-war towns where they can live in simple-minded peace with their isolated surroundings.
Some wanderers even speak of outright friendly super mutant companions who accompany them as friends and equals. Travelers from the East sometimes claim they've met a mutant who walks the highways alone and spouts old-world philosophy. Given their resilience and long lives, these benevolent creatures could still be out there looking for new adventures and traveling companions.
A few diverse communities consisting of humans, ghouls and mutants alike have popped up - at least for a time. Despite the best efforts to get along, it seems that differences will always reduce people to fighting among themselves. Perhaps that Dark God was right, and what the wasteland really needs is more unity.
If the super mutants do ever form another army, they're likely to find the wasteland a little more of a challenge this time around. Since their master fell, the world has become a more dangerous place, and there are other would-be tyrants out there ready to challenge any newcomers.