Aaron "Hotch" Hotchner: You're greedy and narcissistic. You want the recognition...from the book...the fame...like (Ted) Bundy.
George "The Boston Reaper" Foyet: I wanna be bigger than Bundy.
Hotch:...You're the serial killer.
Foyet: That's right.While the BAU has faced all manner of bad guys, both recurring and ones from only a single episode, the following have stood out.
- 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 Cally from "The Tribe" is a chilling example of what you get when you combine extreme sociopathy, charisma, and bigotry into one man. 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 from them. He first sends his cult to massacre the residents of a college dormitory built on former Apache land 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" views homeless people as subhumans who should be exterminated, so he kidnaps them and brings them to his torture chamber, where he puts them through agonizing physical and mental torment before dissecting them alive. He has been killing for a long time, with over 60 victims. Holcombe even gives them the opportunity to escape by telling them they can leave if they make it out in a certain amount of time, but if they manage to do it, he knocks them out with gas to avoid their escape. His last words are "Just let me do my job!"
- As one of the show's few recurring villains, George Foyet, aka The Boston Reaper, had ample time to establish his monster credentials. Disappearing after a long, unsolved killing spree, The Reaper 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 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, driven by an obsessive desire for fame and control, and needing a nemesis in order to function properly, The Reaper 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," profiled as a "human predator", 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 makes an average Dirty Cop look like an angel.
- Shane Wyland from "Into the Woods" is a prolific Serial Killer and Serial 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 a rather different kind of monster from most of those on this list. The head of a human trafficking ring, Lucy has her gang kidnap young men and women and pimp them out to Snuff Film aficionados and other 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 one in charge. 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, her right-hand man, 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.
- Benjamin "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 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 crooked real estate developer who hires crooks to commit crimes in neighborhoods so people will leave them and he can buy up their property dirt-cheap, not caring in the slightest about who gets hurt. One of these families, the Mills, had the father and daughter killed and the mother left in a coma. He then recruits the survivor Trevor into his mayoral campaign, to add fuel to his blatantly racist platform. He has him murder entire families—including a baby in one case—then kill drugged black and Hispanic people with the family’s gun and pin it on them.
- J.B. Allen from "Foundation" is a construction foreman who targets little boys who watched his employees at work. He abducts Angel Suarez, rapes and tortures him for years on end, and when he escapes he is found with dozens of bite marks; the fact that Allen had to get his teeth recapped is further proof of his brutality. He then finds another victim, Billy Henderson, who he tries to murder by burying alive. He had also done these things to a previous victim, and the trophies he gives his daughter implies that he had dozens more.
- Alex Zorgen, while not a Serial Killer himself, 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 "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.