In the world of Fallout, the wastelands are almost totally overrun with mutated abominations that would think nothing of making you their next meal. One of the most infamous of these creatures are the Super Mutants. These giant green monsters were once humans; now, they've mutated into violent, Hulk-like creatures.
Unlike most other wasteland creatures, the Super Mutants were not a result of the bombs' nuclear fallout. During the war between the United States and China before the apocalypse in 2077, many branches of the government and some private corporations were tasked with developing breakthroughs to gain an edge over the enemy. One project was the Forced Evolutionary Virus, an artificially-created virus by West Tek originally meant to protect against various forms of biological warfare. When its true potential became apparent, the project relocated to the Mariposa Military Base in the Midwest, hoping to create the ultimate super soldiers.
The humans the FEV was tested on exhibited superior physical prowess, resistance to combat damage, aging, disease and high levels of radiation. However, these mutants often became much less intelligent and extremely violent to anyone and anything that wasn’t one of them. Additionally, their transformations resulted in losing all their reproductive organs, making them genderless and sterile. This means Super Mutants can’t reproduce naturally, and the only way to make more was by transforming more humans using the virus.
Before the scientists at Mariposa could complete their research, the local garrison led by Captain Roger Maxon discovered the truth about their work and learned they were subjecting prisoners of war to the FEV. Horrified, they rebelled and executed the research staff, sealing away the FEV before eventually making their way to the Lost Hills Bunker to form the Brotherhood of Steel. Until the events that led to the creation of the first real Super Mutant army, the base would lie abandoned for decades.
In 2102, an expedition to Mariposa was led by a Hub merchant named Harold and a former Vault Dweller named Richard Grey. When they broke in, they were attacked by the base's automated security, as well as some surviving mutates. Everyone on the team was killed except for Harold, who was injured but managed to escape, and Grey, who was accidentally knocked into one of the vats of FEV. His prolonged exposure to the virus led him to become a horribly mutated mass of flesh but with vastly increased intelligence, reborn as The Master. Further mutations gave him the ability to neuro link with computers, allowing him to access the base's databanks.
Through experimentation, he managed to create new Super Mutants, some of whom still retained their intelligence. Believing that these Mutants were the only ones who could ever survive in the wasteland, he began efforts to build an army by kidnapping human settlers and transforming them, using a doomsday cult of human followers as a front operation. However, these efforts were foiled by the timely intervention of the Vault Dweller and the Brotherhood, who led an attack on their base of Mariposa and destroyed it, killing the Master.
With the Master dead and most of his army hunted down by the Brotherhood, Super Mutants fled into the wasteland to try and build new lives for themselves. One such effort was made by the intelligent mutant Marcus, and surprisingly, a Brotherhood Paladin named Jacob. Despite being enemies, they soon became great friends, founding Broken Hills as a haven for humans, ghouls and mutants to live in harmony. Marcus was later recruited by the Chosen One to join his quest to save his tribe and the rest of the wasteland from the Enclave.
When the Enclave reemerged in 2241, they tried to use the FEV to aid in global genocide by modifying it to kill anything with mutated DNA. Using captured NCR settlers forced into slavery, they excavated the ruins of Mariposa to find the remaining vats of FEV. Their testing also led to the transformation of an Enclave soldier named Frank Horrigan into a powerful Super Mutant hybrid. Before they could deploy the modified strain, the Chosen One infiltrated their HQ and destroyed the base along with their stockpile.
Afterward, with no more FEV to be found in the West, Super Mutants became increasingly rare to encounter. Despite efforts to integrate into human communities, many were still distrustful of or xenophobic towards Mutants. In the Mojave, Jacobstown was founded to provide safety to mutants and treatment to those still suffering from psychosis and aggression.
While Mariposa was the main research center for FEV, it wasn’t the only place in the country containing the infamous virus. In locations such as the Capital Wasteland, the Commonwealth and Appalachia, scientists had their own stores of FEV, which they used to experiment on various subjects. These Super Mutants were mostly the same as their West Coast counterparts, except that the oldest ones continued to grow, becoming powerful behemoths. They also had no clear leadership structure and were much less organized, mainly due to intelligent mutants being much rarer. Despite this, they were still a grave threat in their respective regions.
The Capital Wasteland Mutants originated from Vault 88, which experimented upon their residents with FEV. The local Brotherhood chapter led a 20-year long war to contain them before finally learning where they originated and destroying the Vault in 2277. At this time, the Enclave had also reemerged, wishing to continue their plans of killing anything mutated. Fortunately, its efforts were stopped by the Lone Wanderer and the Brotherhood while also destroying the last known sample of the modified FEV.
In the Commonwealth, the Institute somehow had their own supply of the FEV and began an effort to create a new breed of Mutants who would act as laborers and soldiers on the surface. While the researchers later refocused on developing advanced synths for these roles, the Institute continued kidnapping settlers and transforming them into Mutants before releasing them into the wild. It is never explained why, but many speculate the Institute did this to keep the Commonwealth factions divided and unable to organize enough to challenge them.
It is generally believed that there is no cure for those transformed into Super Mutants; however, this theory was debunked through the actions of Dr. Brian Virgil. A former Institute researcher, Vergil transformed himself into a Super Mutant and fled into exile in the Glowing Sea. In 2287, Virgil created a serum that successfully reverted the mutation, restoring him to human form. However, the cure was tailored to the specific strain of FEV that he infected himself with, and generalizing the formula to cure anyone else could take decades.
Despite their infamy throughout the wasteland, there have been a handful of Super Mutants that rose above their aggression, striving to do good. Some Mutants such as Marcus, Fawkes and Strong even became loyal and powerful allies to legendary wasteland heroes throughout history.