Monster / Fallout

The Courier: "You want to attack NCR? All of NCR?"
Father Elijah: "Attack? No, not attack them. Wipe the slate clean. Make the Mojave like it was meant to be... undisturbed by man. I'll send the Cloud, the Holograms. Bring ruin in my hands until only I stand atop the HELIOS One tower again. I'll scour Hoover Dam with the Cloud, rain its walls with spears from the sun... with an army of Old World ghosts behind me, Holograms all. I'll kill them until it's only me, me alone... in a quiet world. In a world that's nothing like what happened at HELIOS One."
Fallout: New Vegas: Dead Money

Complete Monsters from the Fallout franchise.
Fallout 2
  • Frank Horrigan is a Secret Service agent and Dragon-in-Chief to President Dick Richardson. A psychopath even before his mutation, Horrigan delighted in killing whenever he could. His first onscreen appearance has him gunning down a family, including their child, for refusing his demands. Later, he gleefully kills Brotherhood of Steel agent, Matt, and wipes out the entire community of peaceful, talking deathclaws that the player had earlier befriended. Horrigan has a special hatred for "mutants", humans and creatures that have been exposed to the FEV virus or even the slightest amount of radiation. This racism leads to him aiding in the Enclave’s plan to unleash a biological weapon which will wipe out all mutated life in North America, in order to make America "genetically pure." Once defeated, Horrigan tries to activate the Enclave Oil Rig's self-destruct sequence, condemning all of his remaining allies to death, just so he can take the Chosen One with him when he dies.

Fallout 3
  • Dr. Stanislaus Braun is the Overseer of Vault 112 who controls the virtual reality simulation where he and the other vault members reside. A sadist with a god complex, for the past 200 years he’s been entertaining himself by torturing and killing every person inside the simulation, only to bring them back to life to torment and kill them over and over again. He specifically mentions that doing so is only fun because they are real people, and not computer simulations. Before Braun allows the Lone Wanderer to leave the simulation, he forces the player to do increasingly horrible things to the other Vault residents, culminating in the deaths of all inhabitants by the player’s hands. Braun was also the Director of the "Societal Preservation Program," better known as the Vault experiments. Advertised as providing civilians shelter from the expected nuclear war, in actuality the purpose of the Vaults was to gather unknowing, human guinea pigs to conduct horrific experiments on For Science!. These experiments include forcibly turning Vault citizens into Super Mutants, tricking people into ritualistically sacrificing their fellow citizens, pumping hallucinogenic drugs into their ventilation system, and driving people insane by implanting posthypnotic combat suggestions into their minds through white-noise. Most of the Vault experiments resulted in the deaths, or worse, of everyone involved with them.
  • Roy Phillips is a rabid anti-human bigot trying to get into Tenpenny Tower through any means possible. When first approached, Phillips's initial plan is to use his feral ghouls to overrun Tenpenny Tower and slaughter everyone inside. Despite this, Roy feels no empathy for his feral brethren, believing them to be mindless freaks only good as guard dogs and cannon fodder. However, if the Lone Wanderer is able to come to a solution where the ghouls are peacefully allowed to move into Tenpenny Tower, Roy will seemingly relent hostilities, at least until a few days later where it's revealed he slaughtered everyone in the Tower anyway, regardless of whether they were anti-ghoul or not, for no reason. When confronted about this, Roy shows no guilt and tells the Wanderer to piss off before he murders the Wanderer too. Furthermore, if Burke is still alive and still plans on nuking Megaton, Roy will fully support Burke's plan so he can see that "smoothskin shithole" wiped off the earth.

Fallout: New Vegas
  • Vulpes Inculta, leader of the Legion's Frumentarii spy network, engages in shady tactics that even Legate Lanius considers highly dishonorable. At one time when the Courier meets him, he razed Nipton to the ground note , enslaving, executing and crucifying most of the inhabitants while coldly imploring the Courier to examine it in detail before informing the NCR of his presence. He also coordinated a nuclear attack on Camp Searchlight, leaving it desolate and turning many of the surviving inhabitants into feral ghouls, and he was secretly arranging with the Omerta bosses to chlorine bomb New Vegas.
  • Cook-Cook is an Ax-Crazy Fiend. The Fiends are a violent bunch of psychos who torture people for fun, but Cook-Cook is so bad that he is barely tolerated even by the other Fiends. He alternates between burning people alive and raping them, such as he did with Corporal Betsy and Pretty Sarah, the latter of whom he disfigured via burning. Two Westsider slavers, who only stopped raping their slaves because it lowered their value, were disgusted when Cook-Cook didn't even wait for them to turn around before enjoying a family he bought from them, starting with their son. One time, he bought some teenage slaves, 3 girls and a boy. The boy was burned alive and the girls made to watch. He is also implied to be a cannibal.
  • Nero and his right-hand-man Big Sal are the Omerta family bosses. The only rule the Omertas have is "don't go against the family," which is punishable by death, but rather than emphasize loyalty, it is instead intended to keep others from standing in the way of the bosses' plans. Such plans involve secretly working for Caesar's Legion to massacre the entire population in New Vegas as soon as the battle at Hoover Dam begins, with a promise that they'll have control over the city. They are selling out the Mojave to the Legion not because they agree with Caesar's ideals, but because of lust for power and loathing of Mr. House for what they perceive to be his lording over them. They also framed a man for murder to blackmail him into working for them, get their prostitutes addicted to drugs to force them to be dependent upon their bosses, and give them to Clanden to be raped, tortured and killed.
  • Clanden, an operative working with the Omertas, at first seems like a perfectly normal, friendly man, but he is in fact a Serial Killer who makes snuff films of himself raping and torturing women to death. In exchange for a constant supply of hookers to kill, he makes chlorine bombs for the Omertas to use in their attack on New Vegas. If the player blackmails him into leaving New Vegas he’ll be okay with it, saying he can always "find more girls to play with" elsewhere.
  • Father Elijah is the former elder of the Mojave Brotherhood of Steel and the Big Bad of the Dead Money expansion. His obsession with old-world technology led to him getting his people slaughtered at the battle for HELIOS. After fleeing the battle, he sought out the fabled Sierra Madre Casino, a treasure-trove of lost technology which he wanted to use to "wipe the slate clean." In order to obtain the casino's treasures, he kidnapped dozens of people, attached slave collars to their necks, and blew their heads off unless they acted as Cannon Fodder for the Sierra Madre’s defenses. Once the Player Character reaches the Sierra Madre, Elijah orders him/her to kill off the allies that had helped them, and later tries to kill the Courier him/herself for outliving their usefulness. Elijah’s ultimate goal is to use the Sierra Madre’s technology to kill off every person in the Mojave, and then build a new nation where every person will be collared and forced to obey him.

Fallout 4
  • Nisha from the "Nuka-World" DLC is the leader of the Disciples, a raider gang defined by their wanton bloodlust and "kill or be killed" mentality. Raised by a raider who "accidentally" murdered her parents, one day he abandoned her for dead. Desiring neither justice for her dead parents nor vengeance for his betrayal, Nisha instead killed him because of his cowardice. Murdering the gang members who refused to follow her, Nisha took over the group and transformed it from a traditional raider gang into a band of psychopathic monsters who engage in torture and murder for their own sake. Her base, and even her own home, are decorated with the dismembered corpses of her and her gang's victims, arranged with a sickening artistry. Cages filled with the gore of past victims are outside her room, and living victims are left chained to the walls, begging for freedom as they know the fate that awaits them. Though the Disciples have an uneasy alliance with the other raider gangs, the Operators and the Pack, Nisha doesn't care if her followers murder rival gang members, only that they aren't caught afterwards. If a Disciple is caught breaking the peace, she deals with them personally. Nisha's greatest contribution to Nuka-World is the Gauntlet, a Death Course which unsuspecting people were thrown into to die horrible deaths for the raiders' amusement. Under Nisha and her gang, the Gauntlet was "improved" to make it more deadly, and more enjoyable for the raiders to watch. Nisha's even pleased when the slaves they send in to clean the Gauntlet die in the process. Even in a community of vile, mass-murdering raiders, Nisha managed to stand out as an Ax-Crazy psychopath who even her raider allies thought was insane.