Complete Monster/Fallout

"Endgame Narrator (Ron Perlman): Myron died less than a year after the defeat of the Enclave, stabbed by a Jet addict while drinking in the Den. His discovery of Jet was quickly forgotten, and now there is no one who remembers his name."
 * The Fallout series has many, many evil people, but Dr. Stanislaus Braun really takes the cake. He is found inside a virtual reality simulation, having been the sole administrator for 200 years. What has he been doing all this time? Why, torturing and killing the others in the simulation and reviving them over and over again of course! He specifically mentions that doing so is only fun because they are real people and not computer simulations, and will be furious if you mercy kill them by claiming that you've ruined his fun. When you meet him, he decides to use you to carry out a series of horrible acts ranging from tricking a small boy into thinking that his parents are divorcing because of him, to breaking apart a happy marriage, to murdering many other people while dressed up as a notorious serial killer. This is just one of the many ways he's tortured the people of Vault 112 throughout the years though, and it goes to show just how screwed up of a guy he is.
 * Roy Phillips is a bigoted Ghoul with a homicidal hatred for humans. Whenever you first encounter him, he's planning on breaking into Tenpenny Tower with his small group of sentient ghouls and a pack of deranged feral ghouls in order to wipe out the humans who live inside. You can choose to help him out and take part in the slaughter, or you can talk him into seeing if you can come to a peaceful agreement by negotiating with Alistair Tenpenny which he will actually agree to. If the Lone Wanderer successfully negotiates with Tenpenny and his tenants to let the ghouls move in, eventually upon returning to Tenpenny Tower, all the human residents have vanished. Should Burke still be alive and nuke Megaton, Phillips will be ecstatic seeing “that smoothskin shithole” wiped out and offer Burke employment.
 * One thing worth noting about Roy is that for all his talk about Ghoul equality, he doesn't care at all in the slightest about the fact that you likely had to mow your way through dozens of Feral Ghouls to get to him. He dismisses them as mindless freaks that are more or less supposed to serve as distractions for intruders showing that his sociopathic lack of empathy even extends to his own people.
 * In Fallout 2 we have the figuratively and literally monstrous Frank Horrigan, a Secret Service agent and The Dragon 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 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 despite the fact that he himself is a 12-foot tall nigh-unkillable Super Mutant himself. 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." And once you defeat him in the final boss fight, he'll simply laugh at you and trigger the Enclave's Oil Rig base's self-destruct mechanism in a last ditch effort to take you down, even if it involves condemning his allies to certain death.
 * A minor but interesting detail about Frank Horrigan that cements his status as a monster further is the fact that he's the only final boss in the series who can't be talked out of his plan. The Master, Colonel Autumn, and even Legate Lanius are able to be bargained and reasoned with, Horrigan flat-out refuses to back down from wiping out the people he perceives as impure and will stop at nothing to tear you to pieces.
 * Also from Fallout 2, we have the slimy little teen chemist Myron. He developed the highly addictive and dangerous drug "Jet" for the Mordino crime family in exchange for money and whores. How did he develop said drug? He conducted experiments on around a hundred slaves suffering from heart conditions, resulting in death by cardiac arrest for nearly all of them until he got the recipe right. If you call him out on this, he'll openly wonder why you care about the lives of the slaves anyway due to him writing them off as disposable guinea-pigs. He even takes pride in how many lives his drug has ruined, and will never stop bragging about it. Fortunately, in the epilogue, he gets one of the most appropriate Karmic Deaths in the history of fiction.


 * There's also the fact that the creep is also a rapist. If you're playing as a female Chosen One with a very low amount of intelligence, he'll give you a spiked drink and then proceed to rape you while you're out cold.
 * Fallout: New Vegas: Cook-Cook of the Fiends. The Fiends themselves are choatic Jerkass types who torture people for fun, but Cook-Cook is so bad that he is barely tolerated by even the other fiends. He alternates between burning people alive, cooking (quite well apparantly), and rape. Two Westsiders, who made a profit kidnapping refugees and selling them to just about everyone (and stopped raping them because it lowered their value), were squicked when this guy didn't even wait for them to turn around before enjoying a family he brought 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. To say nothing of his implied cannibalism and what this could further implicate about that incident...........
 * Big Sal and Nero, 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 they lust for power and loathe Mr. House for what they perceive to be his lording over them. They also get their prostitutes addicted to drugs to force them to be dependent upon their bosses, framed a man for murder to blackmail him into working for them, and give their hookers to Clanden to be raped, tortured and killed.
 * Special mention must go to their man
 * Vulpes Inculta, leader of the Legion's Frumentarii spy network. He 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*, 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.
 * Father Elijah from Dead Money. He was the former elder of the Mojave Wasteland Brotherhood of Steel, and the one responsible for them all getting slaughtered at HELIOS. He fled from the battle and eventually reached a fortress of technology called the "Sierra Madre". However, to access the technology he needed, he had to go through a bunch of defenses like laser turrets, invincible holograms, a big cloud of poisonous gas appropriately refered to as "The Cloud", and an army of Ghost People. So what does he do? Go through it himself? No, he enslaves a nightkin named "Dog"(who is severely mentally impaired, even by nightkin standards, to the point that he has developed a seperate personality known as "God"), and proceeds to force him to kidnap dozens of people to act as cannon fodder for the security of the Sierra Madre, threatening to blow their heads off with his slave collars if they tried to escape (and if the headless corpses by the entrance are any indication, he did just that several times). He then captures you, and he forces you through all the same things as others, except he gives you the help of a team of the other people he captured. You surprise him and eventually reach the Sierra Madre casino, where all this tech he is looking for is located. So then what does he do? He orders you to kill off your former team, simply because they are of no use to him anymore. When you've done that (or haven't, and simply convinced them to leave), you reach what he was looking for: The Sierra Madre vault, and it is here that he reveals his true plan: To unleash the Cloud upon the Mojave, killing every single person there (or "wipe the slate clean", as he calls it), then using the invincible holograms and the other tech to build a new nation, a new nation where everyone has a slave collar slapped on them, so they won't think if disobeying him. Then, to finish off his grand plan, he tries to kill you, despite your loyal service to him. Needless to say, blowing his head off or locking him in the Sierra Madre vault until he starves to death is very, very satisfying.
 * Salt-Upon-Wounds, the leader of the White Legs from the DLC Honest Hearts. He and his tribe of powerful warriors really wanted to join the Legion. The Legion agreed to let them in, but they had to accomplish one task first: destroy the peaceful town of New Canaan. How did Salt-Upon-Wounds and his warriors go about this? They burned the surrounding communities to the ground, took advantage of the New Canaanites kindness to get them to let the White Legs into the town (since they couldn't take the New Canannites in a straight up fight) while pretending they were refugees, then they killed everyone there. The old and sick were butchered as they tried to leave. Priests were burned alive in churches. The children were beaten to death with clubs as they slept. Once you figure out about all this, it's really difficult not to take the "Crush The White Legs" option and kill every last one of these bastards, Salt-Upon-Wounds included.
 * Also he waited to do this while most of New Canaanites who could fight back were out, inclucing the person they were order to kill! In fact he was the only one they really needed to kill.
 * Mr. Burke in Fallout 3. His boss, Allistair Tenpenny, sent him off to set off Megaton's undetonated nuke after evacuating the town and the immediate area of people (not exactly a saintly thing to do on Tenpenny's part, but he at least wanted to avoid killing people). Burke, however, decided to ignore the "evacuate the people" part and was planning on just nuking the town with the innocent people still there. Should you rat him out to Sheriff Lucas Simms, he'll shoot the man in the back while he's not looking and send a goon squad after you for interfering with his plans. And to make things worse? If you help the aforementioned Roy Phillips take over Tenpenny Tower and you haven't detonated the nuke yet, he'll blow up the place anyway even though that due to Tenpenny dying there's no reason to do so anymore! It's worth noting that even Roy Phillips is terrified of him.
 * It's worth noting however that if you're playing as a female Lone Wanderer and you have the Black Widow perk, you can make him fall in love with you. This not only causes him to give up on nuking Megaton, but the guy will also write romantic letters to you. The fact that he can be redeemed if you happen to be female and possessing the perk may save him from being a Complete Monster, but he still remains a loathsome bastard any other time since he's otherwise dead set on blowing Megaton sky-high making his status purely player-dependent.
 * Also from Fallout 3, there's Slaver leader Eulogy Jones. While the man is smooth and polite, it doesn't change the fact that he's the boss of a huge human trafficking ring and keeps his slaves as well as other slavers in line through fear and menace. He has people bought to him, even children to be auctioned off for manual labor, sexual services and the like, and keeps them in horrible living conditions while having them stuck with a detonator collar around their necks that will blow up if they try to run away. If anything, his polite behavior makes him even more deplorable due to the fact that he treats buying and selling innocent people as mere business transactions as they were new cars and the like. While pretty much every slaver is deplorable given their line of work, Eulogy is the worst for being the ringleader for this entire operation.
 * from The Pitt.