For your average bloodthirsty maniac, the greatest challenge they face will be making sure Johnny Law doesn't catch up with them. They'll have to take great care covering up the evidence of their crimes and either fleeing or fighting when the cops or the Vigilante Man show up.
All this becomes a lot easier when they've got a Friend to Psychos on their side. This friend is someone who, while not a homicidal maniac themselves (at least not outwardly, since it's possible to be an extremely low-key psychopath), helps a maniac get away with their rampages. There are basically four variants of this character type. Here they are in order from most to least powerful...
Type I has some ultimate goal in mind, which could be anything from finding buried treasure to running for political office to defeating some particularly implacable foe. No matter what it is, this guy needs all the help he can get - and he's not very picky about where this help comes from, as long as his pals get results.
Type II is vicious and full of hate, perhaps even to the point of being a psychopath himself. But, either because he has a reputation to maintain or because he lacks the will to do anything really heinous, he can't pull off any atrocities on his own. So he's happy to have a more shameless psycho do the dirty work for him.
Type III is a family member or loved one of the psycho, and is being stubbornly loyal. The friend may hope to cure the psycho or at least prevent keep him from getting into (more) trouble.
Type IV genuinely wants to be friends with the psycho, either because he finds some facet or another of his personality fascinating (this can include outright romance and/or sexual attraction) or because he craves the celebrity status that will come with hanging out with a notorious criminal.
Whatever the case, expect the Friend to Psychos to be responsible for throwing the police off the trail, disposing of bodies, giving the psycho a place to hide, and fighting The Hero when they come to take the psycho down. If the character is a Type I or II, expect him to be secretly manipulating the psycho as much as, if not more than, the psycho is manipulating him. Types I and II are extremely unlikely to undergo a HeelFace Turn, and might even play the Smug Snake, taunting the heroes by explaining that since they haven't done anything outwardly illegal, they can't be punished. In fact, villains of these first two types might be so cunning that they won't hesitate to have the psychos stage attacks on them, the better to distance themselves from the psychos in the public mind. Types III and IV are much more likely to be complete dupes of a psycho's machinations and to be pitied by the audience: they're bound to either change their ways after realizing what they have helped to bring about or to be killed or betrayed by the psycho along with everyone else (because, hey, he's a psycho).
On the other hand, if the psycho is trying their best not to be one then a Type III is a very helpful ally to have — such steadfast loyalty can help give the psycho the critical support they need to keep on the path towards dealing with their unwell mind. Types I and II become dangerous obstacles in the psycho's quest to stop being one. Type IV would be more of a crapshoot in this regard, since the motivations of the Friend could be anywhere from benevolent, to well-meaning but in over their head and letting love/infatuation blind them, to just selfish.
Expect this character to be The Comically Serious if their boss or partner is particularly loony. Compare Psycho Supporter, where the friend is just as nuts as his or her boss. Compare Cloudcuckoolander's Minder, the Lighter and Softer version.
- In JoJo's Bizarre Adventure, Yoshihiro Kira is type III: He is the father of serial killer Yoshikage Kira, and insists on helping his son no matter what he does. Even when Yoshihiro dies, he uses his Stand Atom Heart Father to assist his son as a ghost.
- Everyone in various arcs of Higurashi: When They Cry. Friends will help you move, but only best friends will help you move bodies.
- In Descendants of Darkness there's Mibu Oriya, an old friend of Muraki. He covers up for Muraki, gives him a place to stay, and even disposes the bodies sometimes.
- Shinra Kishitani in Durarara!!. His only friends are Shizuo; a man with incredible strength and rages known for causing mass damage, and Izaya; a complete psychopath who expresses his love for humanity (minus Shizuo) by manipulating everyone to gauge their reactions. Shinra is the only person Izaya genuinely cares for and one of the few with a slightly lower likelihood of Shizuo hitting them. However, despite being friends with them since childhood, Shinra couldn't care less if they died as long as Celty was there.
- In the Izaya Orihara spin-off, Daisuke Sozoro and Nec appear to be this. Neither are fans of Izaya, the only reason they actually go along with Izaya's batshit crazy schemes is due to personal debts to him and the very large pay checks they receive.
- Two Sin City stories feature serial killers who get away with their crimes for so long because members of the influential Roarke family are protecting them. In That Yellow Bastard, Junior is able to get away with raping, torturing, and killing hundreds of children over a very long career because his father is Senator Roarke, a man with the entire Basin City government in his pocket. And in The Hard Goodbye, the cannibalistic Kevin has his crimes covered up by Senator Roarke's brother, the even more powerful Cardinal Roarke, who seems to believe Kevin was somehow chosen by God to eat prostitutes' souls.
- The infamous story "Horror We? How's Bayou?" from EC's The Haunt of Fear has a meek old man named Sidney acting as one of these for his brother Everett. Everett is a giant, lumbering maniac who must be supplied with victims to slake his bloodlust. Out of fear for his own safety, Sidney has set up signs to lead people off the main road and right to their doorstep where they are killed and dismembered by Everett and then dumped in the swamp by Sidney. All goes well until one night when all of Everett's victims reanimate and climb out of the swamp for revenge.
- The one-shot Batman comic Joker: Devil's Advocate has The Joker going way over the line, murdering a number of innocent Gothamites with poisoned postage stamps because the post office refused to put his image on any of the new stamps honoring famous comedians. For the first time in his life, the Joker isn't automatically sent to Arkham Asylum when he is captured by Batman, but is found mentally fit to stand trial and has to hire a lawyer to defend him. The lawyer in question does not truly sympathize with the Joker but is only doing his job, and although he's pretty no-nonsense himself he agrees to do anything - within reason - that his client asks of him, including writing his letter of appeals in crayon (and it had to be a lavender crayon).
- Speaking of the Joker, one of his most reoccuring allies in crossovers is none another than Lex Luthor. Despite the bickering and the two being on rather opposite ends, they work commonly well together and oddly get along. For Lex, it is partly pragmatic, knowing that not including the Joker may offend the Clown Prince of Crime and have him mess with your plans, hence why to have him on board.
- The Indiana Jones movie series:
Walter Donovan: You could go down in history.Indiana Jones: As what? A Nazi stooge, like you?Donovan: The Nazis - is that the limit of your vision? The Nazis want to write themselves into the Grail legend, take on the world. Well, they're welcome to it. But I want the Grail itself - the cup that gives everlasting life. Hitler can have the world, but he can't take it with him. I'm going to be drinking my own health after he's gone the way of the dodo.andElsa: I believe in the Grail, not the swastika.Indy: You stood up to be counted with the enemies of everything the Grail stands for; who gives a damn what you believe?!
- René Belloq, the French Jerk archaeologist in Raiders of the Lost Ark, is no Nazi, and has no qualms about performing a traditional Jewish ceremony and even wearing Mosaic priestly garb to open The Ark of the Covenant, even if his Nazi allies have them. All Belloq cares about is proving that he's superior to Indiana Jones in every possible way - and if this means turning traitor, then so be it.
- In Indiana Jones and the Last Crusade, Walter Donovan and Elsa Schneider also cooperate with the Nazis in their search for the Holy Grail for their own selfish reasons: becoming literally immortal and (like Belloq) proving she's a great archaeologist, respectively. Donovan doesn't care if the Nazis succeed in conquering the world or not, while Dr. Schneider actually despises the Nazis but is willing to work with them because they have an inside track to finding the Grail. Both characters lampshade their Friend To Psychos status in dialogue with Indy.
- Mississippi Burning has Clayton Townley, a local political leader who wears a suit and is careful never to be seen in the company of Ku Klux Klansmen, let alone actually participate in their atrocities. But he's in on the conspiracy to cover up the murder of three Northern civil-rights workers in 1964. He really doesn't like it when people try to link him to the Klan. When the conspirators are finally rounded up and punished at the end of the film, he gets a lighter sentence than the actual killers.
News reporter: Are you, sir, a spokesman for the White Knights of the Ku Klux Klan?Townley: I told you - I'm a businessman. I'm also a Mississippian, and an American! And I'm getting sick and tired of the way us Mississippians are getting our views distorted by you newsmen and on the TV!
- Irina Karamanlis from The Anthropophagus Beast aids her insane and cannibalistic brother by disposing of the bodies of his victims, and hiding evidence, though the guilt of doing this ultimately drives her to suicide.
- The gas station attendant from The Hills Have Eyes (2006) sends travellers in the direction of the mutants, and in exchange receives any valuables the victims had on them. He too commits suicide out of guilt by the events of the film.
- The Anti-Hero protagonist of Kalifornia is a self-important yuppie photojournalist who has Condescending Compassion for people with mental illnesses, preferring to study the mentally ill like insects in a glass jar rather than actually help to improve their social conditions. To satisfy his unhealthy desires, he invites two drifters (played by Juliette Lewis and Brad Pitt in one of his rare nonglamorous roles) to accompany himself and his girlfriend on a road trip through the American West. (The girlfriend is quite put off by the other couple, mocking them for looking like Okies, causing the protagonist to scold her for being "prejudiced.") It quickly becomes clear that the two mysterious traveling companions have serious mental problems beyond anything the protagonist could have imagined: the drifter's Tagalong Chick is almost literally a Womanchild, while the drifter himself has an animalistic appetite for violence. As the trip progresses, the photojournalist finds himself sympathizing with the drifter more and more, even to the point of thoroughly enjoying himself when the drifter teaches him how to fire a gun. Things just go downhill from there.
- In Maniac Cop, the villain is a former good cop who was unjustly thrown in jail. After a brutal beating leaves him scarred and brain-damaged, the coroner allows him to be declared dead and escape because he was such a hero. And throughout the film, his former girlfriend helps conceal his rampage.
- Mary Loomis, in Psycho II She is initially sent by her mother Lila to act this part, as part of a scheme to gaslight Norman back to the asylum. However, she eventually falls for him and ends up looking out for him. She even goes so far as to propose going on the run with him, even after she believes he has lost his mind again.
- In Under the Dome, when Junior Rennie is driven by a brain tumor to kill two women, his father "Big Jim" Rennie helps him pin the blame on their mutual enemy Dale Barbara. It helps that Big Jim had a couple corpses of his own he needed to dispose of.
- In the Buffy the Vampire Slayer episode "Beauty & the Beast", Debbie tries to cover for her boyfriend Pete when he starts going through a Jekyll & Hyde situation. She's not very good at it, though. The inevitable contrasts are drawn with Buffy's relationship with Angel, who's just come Back from the Dead after his murderous rampage in Season 2, a fact that Buffy is concealing from her friends.
- This forms the main plot of the third and fourth seasons of Dexter.
- On an episode of The X-Files, Lili Taylor played a blind woman who shared a one-way Psychic Link with a serial killernote and cleaned up his crime scenes after him.
- In Sherlock, Moriarty is first introduced this way, as a "sponsor" for a Serial Killer, as well as having a hand in other crimes. He later gets called a "consulting criminal", who helps untalented crooks get away with ambitious and difficult crimes (as a Foil to Sherlock who is a "consulting detective" who helps police solve difficult crimes). However, it gets subverted upon meeting him face-to-face, where it takes seconds for it to become very apparent that he's far crazier than the people he deals with.
- The Type III family member shows up quite frequently in police procedural shows. Law & Order in particular loves this trope.
- In "My Home Town", on Songs by Tom Lehrer, Tom Lehrer sings nostalgically about the most amazing people in his, well, home town. One of them is
Sam, he was the village idiot
And though it seems a pity, it
He liked to burn down houses just to watch the glow
And nothing could be done
Because he was the mayor's son
- Whenever The Great Khali is cast as a heel, he's accompanied by a normal-sized man in a suit (Khosrow Daivari, Ranjin Singh, Jinder Mahal) who is even more evil than Khali is but outwardly respectable. This man's job is basically to give Khali permission to go on his rampages. Singh was revealed to be actually Khali's brother, so at least he had an excuse.
- Layla El looks like she has become this for AJ Lee. She has explained that her reason for betraying Kaitlyn and allying with AJ was not because she actually sympathizes with AJ, but because she wants more attention for herself. (What makes this spectacularly ironic is that AJ herself descended into madness in the spring of 2012 in order to get more attention.)
- No matter how you play the game in the Mass Effect series; Joker will support Shepard. Prank-call the Council that oversees most of the known universe? He thinks it's awesome.
- Borderlands 2:
- Kreig the Psychopath can ally with any of the non crazies to murder the endless number of foes that you face. The psycho mooks that Kreig is based off of also have allies that range from being just as crazy as they are, to relatively(no one on Pandora is all there) sane. Most notably, Kreig is in love with Maya, one of the other characters. Due to him being a nutjob, he finds it hard to convey his feelings, but he gets "close enough."
- Most of the people on Pandora are Ax-Crazy one way or another, including your NPC allies, so the few relatively grounded characters such as Athena and Roland act as this.
- Roy is kind of like this to Belkar in The Order of the Stick, even putting in a good word to get the psychopathic halfling out of prison. Although in his case, it's more of a case of realizing that the Sociopathic Hero is better off in his charge, where he can keep him 'pointed at the bad guys', rather then placing his bets on the idea that any prison can hold him.
- The Zalia family to Oasis in Sluggy Freelance, though Oasis is more of a Friendly Neighborhood Psychopath than most.
- Batman: The Animated Series,
- With the exception of Harley Quinn, most of the Joker's henchmen didn't seem to share in his psychosis; they largely seemed to be Only in It for the Money, or because they were too scared of the Joker to refuse. The series and its spinoff comics seemed to be aware of this discrepancy sometimes, having the Joker operate alone or with only Harley. In "The Last Laugh", they partially solved the problem by having the chief henchman be literally a mindless robot, which makes it okay for the animators to show Batman "killing" the thug onscreen.
- In the "Baby Doll" episode, Mary Dahl is quite challenged in her criminal activities by literally being the size of a young child, so she usually relies on Mooks to help her out. These include two men with machine guns who, even though they're dressed as Gilligan and the Skipper, don't come across as particularly crazy (or at least not as crazy as Dahl), as well as a full-grown woman in a business suit who doesn't say much and looks quite mousy, but is actually a kung-fu expert.