George "The Boston Reaper" Foyet: You think I'm afraid to die?
Aaron "Hotch" Hotchner: You're greedy and narcissistic. You want the recognition...the fame...like (Ted) Bundy.
Foyet: I wanna be bigger than Bundy.
Hotch: Well, you can't enjoy it if you're dead.
Foyet: If you know me so well then how come so many had to die to bring you here?
Hotch: That's your choice, not mine. You're the serial killer.
Foyet: That's right.The BAU has faced dozens, if not hundreds, of bad guys, both recurring and ones from only a single episode; serial killers, serial rapists and others. A select few are especially vile.
- Karl Arnold, aka The Fox, is the first "family annihilator" to appear in the show. Debuting in "The Fox", Arnold uses his position as a family psychiatrist to seek out families that he feels are dysfunctional—that is, where the father is not the dominant personality—stalks them, and then kidnaps them while the neighbors believe them to be on vacation, using his control over the children to keep the parents hostage. He keeps them separated from one another for days, then brings them together for one last supper, after which The Fox marches the entire family into the basement and kills them, starting with the children and ending with the father. Upon his capture, The Fox explains that he does this because his own family fell apart due to his obsessive-compulsive, controlling nature, and he wants to show how much worse things can get when the head of the household isn't "strong". Any sympathy one might have for him is obviated in his second appearance, in season 5's "Outfoxed." Interviewed by the FBI for help with another family annihilator, Arnold comes off as calm and in control, repeatedly asking to see pictures of the crime scenes, coming onto Prentiss, taunting Hotch for his marital problems, and gloating about the fact that before he killed the families he took hostage, he would beat the male children, and rape the female ones. This revelation, coupled with The Fox's smug, superior demeanor, and the fact that he's become pen pals with the Boston Reaper—laughing as he tells Hotch that The Reaper is coming for he and his family—wipes out any sympathy the viewer might once have held, and cements his status as a true monster.
- Jackson "The Grandfather" Cally, from "The Tribe", is a chilling combination of extreme sociopathy, charisma, and bigotry. A cult leader native to Terra Mesa, a mostly-white New Mexico town known for tensions with a mostly-Apache town nearby, Cally preys on troubled teenagers interested in Native Americans, indoctrinating them into being willing to kill for him under the pretense of "helping" the Apache reclaim all their ancestral land; while keeping his true goal, attempting to foment a race war that would wipe the Apache out, a secret. He first sends his cult to a college dormitory built on former Apache land, having them massacre the residents in gruesome ways such as decapitation and impalement, mimicking Native American war rituals, in hopes the Apache would be blamed and the whites would retaliate. When the FBI rule out the Apache as suspects, Cally has his men decapitate the leader of a local racist group, his wife, and his two young children and impale their heads on pikes for the FBI to find. His final and most wicked gambit, however, is to dress up his men as members of the racist group and send them on a wholesale massacre of the Apache town's school. When foiled and caught by the FBI, Cally's only justification for his actions is that he hoped to show the world what "savage animals" the Apache people "really" are.
- Charles Holcombe, from "Legacy", is a callous serial killer who is dedicated to wiping out the homeless, junkies, prostitutes, and vagrants, viewing them as subhuman filth that is worthless to society; he has over 60 victims to his name. Using a meat-packing plant he inherited from his late father, Holcombe re-outfitted it into a brutal maze-like Death Course where he forces his victims to play a sadistic game: escape before sundown or die horribly. What follows is his victims being put through horrible physical agony where they're forced to crawl through rooms filled with broken glass, endure being sprayed with gas, and run from hungry attack dogs. The whole time, Holcombe torments his victims with footage of him dissecting his previous victims alive to let them know what to expect if they fail. When his latest victim, a prostitute named Maggie, successfully completes the course, Holcombe reveals that he had no intention of ever letting her escape and knocks her out with a spray of gas before hauling her off to slaughter. Ruthlessly obsessed with his mission to the end, Holcombe's final moments before being gunned down are him attempting to finish off Maggie while screaming "Just let me do my job!"
- Mason Turner, from the two-part season finale "To Hell..." "...And Back", proves to be among the nastiest unsubs the BAU has faced. Unable to hunt and kill his victims himself due to being paralyzed from the neck down, the sadistic and arrogant Mason manipulated his mentally handicapped and freakishly strong brother Lucas into becoming a killing machine. Mason has Lucas drive to Detroit to kidnap transients and haul them back to their pig farm in Canada, where Lucas brutally slaughters them by crushing their neck with a sledgehammer. Mason then guides Lucas through performing pointless, cruel experiments on their remains before discarding them by feeding them to the pigs. And all through the process, Lucas watches through a complex series of mirrors in order to satisfy his sadistic tendencies. Through this process Mason has claimed eighty-nine lives, and is only stopped from killing a ninetieth victim when the BAU raids his farm. In order to throw suspicions off himself, Mason tries to pin his crimes on Lucas, who he encourages the BAU to shoot on sight. Once he's exposed for the monster that he is, Mason is smug and completely unapologetic about his crimes, coldly stating that his victims were worthless trash that should be honored to be a part of something bigger than themselves. With a body count reached by only a few other unsubs, Mason Turner is proof that sometimes a Freudian Excuse isn't enough to justify, or even explain, cruelty.
- George Foyet, aka the Boston Reaper, having disappeared after a long, unsolved killing spree, comes out of retirement in "Omnivore" following the death of Tom Shaunessy, the lead investigator from the original case. Killing two couples, the Reaper baits the BAU into entering the case, then calls up Aaron Hotchner, for whom his original spree was That One Case, offering to stop the killings if Hotch admits defeat and calls off the investigation—the same deal that The Reaper had cut with Shaunessy years ago. When Hotch turns him down, the Reaper massacres an entire bus full of passengers. He later kidnaps a journalist who had written a book about him and demands the man correct the errors in it, most notably suggesting that The Reaper might have died rather than retired; when Hotch captures him, The Reaper reveals that he's done it all in order to be "more famous than they'll ever realize." Breaking out of jail, the Reaper bides his time before ambushing Hotch at home in season 5 premier "Nameless, Faceless," where he tortures him note , then drops him off at the hospital, along with clues that indicate he is going after Hotch's ex-wife, Hayley, and young son, Jack. He does just that in "100". Mutilating and mortally wounding the officer assigned to protect them, he tracks Hayley and Jack to their home, murders Hayley while forcing her to talk to Hotch over the phone, and then gloats to the BAU agent's face that after he's done with Hotch, Jack will be next. Totally self-centered and driven by an obsessive desire for fame and control, George Foyet is Aaron Hotchner's personal nightmare.
- Anita Roycewood, from "Mosley Lane", is a serial kidnapper and child murderer, who forces her submissive husband, Roger, and first kidnap victim, Charlie Hillridge, to help her abduct and imprison children. Keeping the children locked up in a hidden hallway, Anita renames them, dyes their hair, and is implied to sexually abuse them, using fear, beatings, and threats to the other children to keep them in line. When the children grow too old for her liking, or become uncontrollable, Anita knocks them out, in the case of Stephen Shepherd beating him savagely beforehand, places them in a cardboard box, and burns them alive in a crematorium, whistling jauntily the entire time. When the police catch onto her, Anita abandons Roger, and takes the three remaining children, Aimee Lynch, Mae Hall, and Charlie, to the crematorium, where she tries to force Charlie to help her burn the other two; she then intends to kill him. Guilty of some of the most callous crimes yet shown on the show, and viewing her victims as replaceable, Anita's reasons for doing what she does are never explored, leaving only an utterly hateful cipher for the cast and the audience to deal with.
- Deputy Ronald Boyd, from "A Rite of Passage", kills illegal immigrants because it allows him to assert a sense of power that he otherwise lacks. He lies in wait at border crossings, picks out a straggler, and then chases them through the desert on his ATV until they can no longer fight back, finishing them off with his machete. When the Hispanic sheriff, whom Boyd loathes for being new to town, starts looking into the missing illegals, Boyd sends her progressively more aggressive "messages"—severed heads in boxes outside the sheriff's office; a severed head on a pole in her front yard—until he finally kills her for sticking her nose into his business, while ranting that the illegals aren't really missing because "they ain't supposed to be here in the first place". Dismembering her corpse in order to pin the blame on drug kingpin Omar Morales, Boyd proceeds to murder Morales and most of his gang to cover his tracks; also because they're Hispanic. When his partner objects, Boyd shoots him and places the gun in the hands of the dead Morales. Taking offense to the idea that he sees himself as weak, and viewing himself as a total badass, Boyd, profiled as a "human predator", makes an average Dirty Cop look like an angel.
- Shane Wyland, from "Into the Woods", is a prolific killer and rapist of children. Put on parole after the sexual assault of a ten-year-old boy in Harrisburg, Pennsylvania, Shane abandoned civilization in favor of the woods along the Appalachian Trail to make it easier for him to hunt children. After selecting a child, Shane would stalk them before abducting them and imprisoning them in an Abandoned Mine, where he would repeatedly molest them throughout the winter before finally killing them. Shane kidnaps a young boy named Robert, as well as his sister Ana, who Shane intends to kill. While holding them captive within a storage cell, Shane molests Robert. After Ana flees captivity, Shane takes Robert to the hotel of a fellow pedophile, Brandon Stiles, where he offers to allow Stiles an hour alone with Robert in exchange for painkillers to treat his leg injury.
- Lucy, from "Supply and Demand", is the head of a human trafficking ring. She has her gang kidnap young men and women and pimp them out to various sexual deviants, staging live shows in which the victims are tortured, and even killed, by her men and/or clients. The victims are beaten, drugged, and otherwise mistreated to ensure compliance, and are kept caged in between visits from Lucy's clients. A psychological sadist, who derives gratification from being in control, Lucy frequently has her men lock in her in the cages, so that she can enjoy the victims' terror and win their trust while pretending to be a fellow victim; she takes unholy glee in revealing that she is, in fact, The Leader. She's also the one who scouts the victims out in the first place, visiting college campuses, while posing as a student, and then staging her own abduction alongside any students she has befriended. When Lucy discovers that Renee Matlin, one of her victims, is an undercover cop, she proceeds to play a game of Russian Roulette with her, then has the other woman savagely beaten, gloating the whole time. Interrupted by the police, Lucy manipulates Max, one of her associates, into being killed by them, planning to frame him for her crimes. Found out by David Rossi, Lucy's last act is to pull her revolver and try to blow him away.
- Ben "Cy" Bradstone, from "Proof", has a mental disability, which makes him unique, but not even slightly sympathetic. Pretending to be far more handicapped than he is, Cy lures women out of the public eye, forces them into his shed, rapes them, and then stabs them to death. He first stabbed their eyes out, but later evolved to using sulfuric acid to burn away their senses. If they don't like the way he looks, he takes their eyes. If they spit when he kisses them, he takes their sense of taste. If they don't like his smell, he burns out their nostrils. His video journal—which strongly implies many more victims—reveals that he has been like this since he was a young boy, and he gloats that he brutalizes women for the same reason that he used to beat his dog: because it's fun. We eventually discover that he is targeting women who remind him of his sister-in-law, whom he attempted to molest when they were both teenagers. When his niece puts on a cheerleader costume that reminds him of her mother she becomes Cy’s final victim. After his arrest, his brother Matt, who has always been supportive of Cy, going so far as to offer to let him move in with him, demands to know why Cy did this; Cy laughs in his face, and tells him that he has always hated Matt and was planning to deafen and then kill him one day. A ragingly misogynistic psychopath who just happens to be handicapped, Cy is fully aware of how awful his actions are, as evidenced by this message he leaves for Matt:
What I'm going to do to your daughter, you can see on this tape. But what I did to your wife? Now that's a video you should see.
- Clark Preston, from "A Thin Line", is a greedy, crooked real estate developer and one of the show's most infamous proxy killers. He would hire criminals to commit crimes in neighborhoods so people would leave them and he could buy up their property at a much lower price, with him not even caring about who gets hurt in the process. During one of these raids, the Mills family had the father and daughter killed and the mother raped and beaten, leaving her in a coma. He later manipulates and recruits the survivor of the family, Trevor, into his mayoral campaign by brainwashing him with racist ideology as well as using him to help with his mayoral campaign, which he also uses to fuel his racist agenda. He has Trevor kill entire families of people, including young children and even a baby in one case, and would have him then kill drugged black and Hispanic people with the family’s gun and pin it on them in the hope of supporting his plans.
- J.B. Allen, from "Foundation", is the sadistic, pedophilic owner of a construction company who targets little boys who he draws in by letting them play with his construction tools. Once he has a boy in his grasp, Allen continuously rapes and tortures his victim over the years before killing him. One of his victims who was lucky enough to escape, a boy named Angel Suarez, was covered in bite marks and was mentally destroyed by Allen's torture. When he finds another victim to replace Angel, a boy by the name of Billy Henderson, he subjects him to the same torture and attempts to bury him alive. His daughter repressed memories of Allen doing the same to another unnamed boy, and all the trophies he'd pawn off on her in the guise of gifts show that he had dozens of other victims.
- John Curtis serves as the Arch-Enemy of the BAU for the season. Originally a brilliant FBI Special Agent, Curtis, after an incident caused him to be demoted and transferred to Kansas, vowed vengeance on the people responsible. He would become the serial killer known as "The Replicator" where he would copy some of the season's most gruesome murders. These murders include sewing a man's mouth shut before leaving him to die of asphyxiation; sawing off the legs of two people, without the use of anesthesia; dislocating a woman's limbs making her a puppet; and using a hammer to smash a women's head to death. He also manipulated a man whose life was ruined by the BAU into becoming a killer—with 3 victims—only to abandon him once he had outlived his usefulness, driving the man to commit suicide. He later appears in person in "The Replicator", where he forces Erin Strauss, the woman who caused said incident, to drink poisonous wine, causing her to die slowly and painfully. His final plan would then come into motion where he would trap the BAU in one house where he'd set explosions to kill them all, completely uncaring if he is still in the same house. A narcissistic sociopath whose manages to darken an already grim show, John Curtis, who made up in cruelty what he lacked in body count, would do anything to see those he believed had wronged him suffer to the fullest.
- Alex Zorgen runs a human trafficking ring that sells women, regardless of age, to serial killers and other criminals online. In 1993, prior to creating this ring, he abducted a woman named Donna Goldhard, and kept her as a Sex Slave, repeatedly raping and torturing her for the next 22 years. From one of those rapes came a son, named Kyle. In the season premiere "X," Alex, along with his family, kidnaps a woman and uses his website to auction her off to a serial killer. As the season progresses, Alex has Kyle stalk the BAU's newest member, Kate Callahan, by posing as an attractive high school senior online to gain their trust of her niece Meg, and her friend, who are both 14 years old. He sends his wife and son to kidnap them in the season finale "The Hunt," but Kyle only catches Meg. Due to this, Alex murders Kyle, his own son, without showing any remorse and simply moves on with his plan to sell Meg online to a serial killer. He was later arrested by the BAU, but Meg had already been sold. When they ask him where Meg’s captor is keeping her, he refuses to cooperate and just taunts Kate about the things her captor is going to do to her. Having no regard for anyone, not even his own family, and only caring about selling women to his online human trafficking ring and making money out of it, Alex Zorgen is a sociopath in its worst form and among the worst the BAU had to face.
- Hayman Vasher, from "A Thousand Suns" is an aerospace engineer who is a big admirer of Robert Oppenheimer, especially how he progressed from socially-awkward to world-renowned. For Vasher, who after being humiliated on a date dropped out of society, this involved building a device which can hack into airplanes and control them. As a "test", analogous to the Manhattan Project's Trinity test, Vasher makes a plane crash in a sparsely-populated area, resulting in over 150 deaths, including the woman who he had dated. As his Hiroshima, Vasher takes control of a plane with over 300 people and plans to crash it into a populated area. He agrees to let the plane land if the BAU calls off fighter jets which have scrambled to shoot the plane down if necessary, but once this happens, Vasher tries to crash the plane anyway, before he and his device are both shot. Vasher was also looking at other flights, meaning that there might have been still other crashes had he not been stopped. Driven only by his need for attention and enjoying "playing God or some other deity", Hayman Vasher, "a mass annihilator…who wants to eradicate life on a large scale", is one of only a few unsubs to successfully have a triple-digit body count.
- Mitchell Crossford, from "The Witness" is the son of an anti-government cult leader and later adopted this extreme ideology. When his half-brother Theo, with whom he was planning to launch terrorist attacks, started having an affair with a married woman, Crossford, enraged, plotted revenge. He acquired sarin gas from a disgraced chemist—who Mitchell then killed—and placed sarin on a bus the woman usually rode; she wasn't on the bus that day, but 10 other people were killed. While stalking his brother, Crossford saw Charlie, the woman's husband, murder Theo, and manipulated him into becoming his patsy, threatening to report the murder, while also threatening Charlie's 12-year-old daughter. While he may have planned even more attacks, his main goal was using Charlie to launch a larger sarin attack on the FBI building in Los Angeles. Over a thousand people were at risk, before the FBI successfully evacuated the building and sealed the garage where the sarin was placed.