Super Mutant (Fallout 3)

Vault 87 super mutants are Fallout 3 and Fallout: New Vegas's version of the super mutant.

History
These super mutants were created in the Evolutionary Experimentation Program, the experiment assigned to Vault 87. The modified strain of FEV which created these mutants resulted in a new strain of super mutants which, in addition to becoming senile, grow larger and stronger as they age. They are different as they are green-yellow in skin color and less intelligent, but look more "healthy" than the western super mutants, as they are never seen with any cybernetic parts or organic disorders. Every super mutant's facial expression is permanently set in a sneer. However, unlike their counterparts, they are less human, and after the transformation no clues on how they looked in their former lives could be found. They take prisoners to transform them into more super mutants. Just like on the West Coast, the by-product of the Vault 87-based creations are Centaurs, who act as watch/attack dogs.

During exploration of Vault 87, information from a terminal reveals more about the process of mutation that Super Mutants go through, at least when it comes to the specific strain of FEV found in the super mutants of the Capital Wasteland. As a human mutates, its muscular and skeletal systems develop rapidly, while their mental faculties diminish. Most sexual characteristics are eliminated, transforming the subject into an almost asexual state.

Despite their supposed lack of intelligence, even compared to West Coast mutants, they are somehow able to organize themselves into a coordinated army (as evidenced by numerous raids and the attempt to reinforce their positions at the Capitol which led to the attack on GNR), procure large amounts of advanced weapons, ammo, and equipment, and even maintain the FEV infrastructure necessary to transform humans and increase their numbers. How they are able to pull this off is never explained as the player never meets a leader or governing body in the game.

In the ruins of D.C., the super mutants are looking for humans to expand their army and a new source of F.E.V (a conversation between two super mutants in Vault 87 reveals that they are running out of the "green stuff").

Types
The East Coast super mutants are divided in the following categories:

Regular (super mutant)
The youngest and weakest of the Capital Wasteland super mutants. They never walk alone and usually attack in groups led by a stronger super mutant. Regular super mutants have almost twice as much health as most standard human NPCs, but this is somewhat offset by their lack of body armor.
 * Carry Nail Boards, Hunting Rifles, Frag Grenades. They have little to no armor.

Brutes
These super mutants are generally stronger and better armed. They are the most common of all super mutants once you get to a high enough level.
 * Carry Sledgehammers, Assault Rifles, and occasionally Missile Launchers or Miniguns. They also have a crude form of metal armor, making them somewhat tougher.

Masters
The Super Mutant Masters are the group leaders of the mutant army which plagues Capital Wasteland. They have the most Hit Points of all the super mutants (without Broken Steel).
 * Carry Chinese Assault Rifles, Super Sledges, Missile Launchers and Miniguns. Their armor consists of black tubing which wraps around their lower and upper body.

Overlords
The Mutant Overlords are old, powerful super mutants who appear to already be on their way to becoming Behemoths. Their intelligence (in comparison with other types of super mutants) is questionable, but they are smart enough to wield energy weapons. Sometimes they are seen leading groups of super mutants, but they more frequently tend to act alone or in pairs. Overlords also get a 40 unblockable damage bonus to when attacking with a Tri-Beam Laser Rifle and a 25 bonus when attacking with a Super Sledge.
 * Generally carry Tri-Beam Laser Rifles, Super Sledges, Missile Launchers, or Gatling Lasers, although some have been seen carrying a Minigun inside Roosevelt Academy (Confirmed Xbox 360, PC).
 * Overlords can be deemed expensive targets when considering the firepower and ammunition requirements to despatch them, while offering minimal XP and relatively low levels of loot.

Behemoths
The greatest threat among the Eastern super mutants, there are only five of these Behemoths. They are the oldest and the strongest of their kind, being much bigger than any other humanoid creature.
 * Usually armed with rather large Fire Hydrants mounted on the hydrant's water main pipe, used as a makeshift Melee weapon, or they could also just use their enormous fists. Both cause major damage.

Quotes

 * "I'll wear your spine around my NECK, human!" 
 * "Why do you humans ALWAYS FIGHT?!!?" 
 * "Knock knock. Who there? Humans. Humans who? Pitiful humans! Can't evolve!"
 * "What you up to? Something fun? Something to eat? ME BORED!" "Why you care?! You human or something?!" "Never mind! You too dumb to talk to!" - Super Mutant talking with another Super Mutant.
 * "I have a joke for you. Ready? Knock knock. Who there? Humans. Humans who? Kill the humans, kill them ALL HAHAHAHAHA. HAHAHAHAHA Oh that's a good one HAHAHA!"- Super Mutant talking to another Super Mutant.

Fallout: New Vegas
They are seen in Fallout: New Vegas as well, and they have seemed to have been able to make it to Vegas. They are ruled by the crazy Tabitha, and their main base in Vegas is Black Mountain. They are now at war with a similiar super mutant race known as "Nightkin".