These super mutants were created in the "Evolutionary Experimentation Program," the experiment assigned to Vault 87. The modified strain of FEV used to create these super mutants resulted in a new strain of super mutants which, in addition to becoming sterile, grew larger and stronger as they aged.
The first super mutants of this variety were created in 2078, becoming a permanent feature of the Capital Wasteland. Too dumb to overrun it, but too strong to die off.
Like all super mutants, they appear to be powerfully-built, hairless humanoids standing seven to eight feet tall and clad in heavy armor made from car parts and scrap metal. They differ from their Western counterparts in that they possess a yellow-green skin color as opposed to the green or blue colors of their western cousins, as well as thick, bulging veins. They are also generally less intelligent and more aggressive. They also appear more healthy, as they are never seen with any cybernetic implants or organic disorders. However, unlike their distant cousins they retain less of their humanity after transformation, and no distinguishing features from their former lives can be found. Every super mutant talks in a deep, guttural voice that emphasizes each syllable due to their mouths being permanently stuck in a tight, angry sneer. Also, as Fawkes demonstrates when retrieving the GECK in Vault 87, they are highly resistant to radiation.
During exploration of Vault 87, information from terminal entries reveals more about the process that humans go through to become super mutants. When exposed to the specific strain of FEV found there, muscular and skeletal systems develop rapidly, while mental faculties diminish. Like other super mutants, despite having a build similar to a muscular human male, they completely lack functioning genitals, relying on FEV vats to reproduce. Another unique trait of the Vault 87 Super Mutants is that they grow larger as they grow older, and can range from eight to at least twenty or thirty feet in height, the largest of which are known as "Behemoths". These Behemoths seem to be even less intelligent than their smaller brethren, talking only in echoing roars and blindly destroying everything in their path, acting more like an unfettered beast than a soldier.
Despite their apparent lack of intelligence, the mutants are somehow able to organize themselves into a coordinated army (as evident from numerous raids). It seems likely that "might makes right" and the older and larger mutants (who can still think somewhat coherently) are in charge. They have also procured large amounts of advanced weapons, ammunition and equipment, and maintain the FEV infrastructure necessary to transform humans to increase their numbers. How they are able to achieve these things is never explained, as the player never meets a mutant leader or governing body in the game, unlike in previous Fallout games.
In the ruins of D.C., the super mutants are looking for human captives in order to expand their army, as well as a new source of FEV; as a conversation between two super mutants in Vault 87 reveals that they are running out of "green stuff." They also appear to eat humans, as evidenced by the bags of mangled human remains often found in their camps, as well as their threats of eating the Lone Wanderer's corpse often shouted during combat.
Despite their seemingly low intelligence, super mutants can sometimes employ effective military tactics. Melee-armed mutants will move in to engage the player while those behind them take pot-shots with ranged weapons. Super mutants armed with grenades will often use them without regard for any fellow mutants that might be caught in the blast radius.
When encountered at lower levels, super mutants are usually in groups of two or three, accompanied by one or two centaurs, often employed as a sort of a rudimentary attack dog. At higher levels they can be found in groups of three to five, with a few centaurs acting as their watch dogs.
These are the youngest and weakest of the Capital Wasteland super mutants. They are usually encountered in groups of two or three, led by a stronger super mutant. Regular super mutants have almost twice as much health as most standard human non-player characters, but this is somewhat offset by their lack of body armor. Some of their prime locations are the GNR building plaza, the National mall, the Capitol building, the Statesman Hotel, the National Archives, and Falls Church. They can also be found aboard Mothership Zeta in stasis chambers. Freeing them will cause them to become hostile.
Super mutant brutes are stronger and tougher opponents than regular super mutants, as they are better armed and armored. They are most commonly seen once the player character reaches a higher level. Brutes are easily distinguished by their galea-like metal helmets and crudely stylized metal armor.
Until Broken Steel is installed, super mutant masters are considered to be the group leaders of the mutant bands which plague the Capital Wasteland. They have more Hit Points than most "common" super mutants. They are discernible by their armor, which appears to consist of what resembles black tubing that wraps around their lower and upper body and something like a fighter pilot helmet. A gas mask is strapped to their left shoulder, possibly acting as a makeshift pauldron. They are generally never alone and are usually accompanied by one or two brutes.
The super mutant overlords are variants added to the game in Broken Steel. They are aged, even more powerful than super mutant masters, and much harder to bring down. Super mutant overlords appear to be evolving into behemoths, and are about half-way between the normal super mutants and behemoths in size. Their intelligence (in comparison with other types of super mutants) is questionable, but they are smart enough to wield Energy Weapons with some degree of skill. Sometimes, they are seen leading groups of other super mutants, although they are more frequently seen in pairs, if not completely alone. Overlords also have a 40 unblockable damage bonus when attacking with a tri-beam laser rifle and a 25 damage bonus when attacking with a special version of a super sledge. When carrying an assault rifle or a Chinese assault rifle, they use a one-handed pistol animation. They have a good chance of dropping above-average loot such as stimpaks, mini nukes, and purified water.
Towering above any player character, at about 20 feet tall, the behemoths are the greatest threat to humanity found among the Super mutants. There are only five behemoths to be found in the game, although reports of their sightings continue through dialog amongst the Brotherhood of Steel.
These super mutants are the oldest and strongest of their kind. As well as being many times larger than any other humanoid creature, for unknown reasons, they will not speak; instead they will make monstrous roars. They are usually armed with an almost unrealistically large fire hydrant mounted on a large pipe; other than that, they also use their enormous fists. Either way, both weapons are heavy-hitters, and will cause major damage against any enemy smaller than them. They carry a cage made from shopping carts on their backs, used to carry off captured humans to be mutated or devoured later.
If a super mutant picks up a pistol, it will use the same attack animation as an assault rifle, which is a two-handed grip (the front hand is floating in front of the pistol). When shooting the pistol, their hands will shake from the recoil, as if the pistol were automatic.
There is a conversation between two super mutants inside Vault 87 in which they discuss "the green stuff" (FEV) and that Fawkes thinks that men will come to take it away, while his companion says that they will turn the intruders into mutants.
Informing Elder Lyons that the super mutants originated from Vault 87 can gain you some Positive Karma.
After Broken Steel is installed, super mutants become rarer, and finding them will take some effort outside of spawning areas. Some super mutants can be heard talking that the "bucket heads" have been killing too many of them, this being their nickname for the Brotherhood of Steel and\or Enclave.
According to concept art, there were originally three classes: Grunt, Spinebreaker, and Behemoth.
The reason why the fire hydrant and the shield made by a car door of the behemoth is so unrealistic big is that the in-game model of the Behemoth is not in the originally intend size and so when the resize was made those parts got bigger than they should.
pcps3xbox360 Occasionally, super mutant brutes, masters and overlords may appear merely labeled as a "super mutant", but still have the same health and equipment of brutes/masters/overlords. [verified]
pcps3xbox360 Super mutants may not acknowledge the player no matter how close he/she gets to it. [verified]
xbox360 The V.A.T.S headshot chance for Overlords will never display above 74%, though the player will still hit with higher frequency. [verification overdue]