Arthax: That was... Demeaning. Yeagar: I never knew you could storm a castle like this... Nodwick: The thieves' guild would be unstoppable if they invested in blue coveralls with the name "Al" embroidered on them.
Okay, so you have to break into this high tech science lab, or a government facility, or a fancy bank, or something. It doesn't really matter what this place is to you, because it's swarming with security and there's no way you'll ever get in...or is there?
Enter the Janitor Impersonation Infiltration. Custodians, janitors, cleaning ladies, what do these people have in common? They have access to every room in the building and might as well be part of the scenery. No one pays attention to them or wonders what they are doing sneaking around after hours while everyone else in the building is gone. So if you are looking for an easy-in, they are perfect candidates for impersonating when one has to steal that secret formula or those hidden financial records.
Other similar jobs which have the same relative anonymity of the janitor and are Beneath Notice may also qualify for this trope. Being that these people might be secret agents, there's a definite possibility of Almighty Janitor overlap. Compare Dressing as the Enemy, The Infiltration, Room Disservice and Delivery Guy Infiltration. Depending on what is done with the real janitor, may overlap with Mugged for Disguise. If the impersonator seems to do this often in different situations it might be a case of Why Do You Keep Changing Jobs?.
In Megaman NT Warrior, Ms. Madd infiltrates in this manner so that she and Mr. Match can compete again in the N1 Grand Prix.
In Yu-Gi-Oh! 5Ds, Carly infiltrated the Arcadia Movement building by pretending to be a janitor. Divine stopped her and pointed out she was not the usual janitor, but she claimed he was sick.
In Blood+, the Red Shield must dispatch a chiropteran that has appeared around a Vietnamese all-girls' boarding school while being covert about it, partially because they're able to pose as normal humans. To do this, Saya, the only member of the team who is able to kill the chiropteran, poses as a student, while her bodyguard Hagi poses as the school gardener (only to mostly fail at not attracting attention due to his good looks).
Chameleon does this in the very first issue of The Amazing Spider-Man, leaving the real janitor bound and gagged in a closet.
Used in an issue of Catwoman when Selina infiltrates a police station. One cop even mentions that the cleaning lady is supposed to have the day off, but doesn't pursue the inconsistency beyond that.
She did the same thing in another issue by posing as a maintenance worker. She lured the real maintenance worker to an apartment, where she left him Bound and Gagged in a closet after stealing his uniform and van.
Taking a leaf from The Shadow's book (see below), the Batman has also masqueraded as the janitor at police headquarters. Sometimes his disguise amounts to a mop and overalls, a hat and a fake beard over his Batman costume.
In Huntress #5 (the 2012 mini-series), Helena disguises herself as a cleaning woman to sneak into the Lion's fortress.
Scarlett attempts it in the No Dialogue Episode "Hush Job" in G.I. Joe Yearbook #3. In an attempt to rescue Snake-Eyes, she sneaks into Cobra HQ disguised as a cleaning woman, with Snake-Eyes' wolf Timber hidden inside a cannister vacuum cleaning. However, the Cobra sensors pick up the huge amount of weaponry she is carrying and she is exposed.
XXXenophile: In "R.U.R. or Are You Ain't My Baby?", a female spy disguises herself as a cleaning woman to infiltrate a robotics lab and destroy the prototype robot being developed. (By sexing it to death).
In Zoolander, Derek and Hansel try to steal proof that Mugatu is trying to have Derek assassinate the Malaysian Prime Minister by dressing up as Janitors. They dubbed the character voices onto completely different actors because Derek's makeup skills are just that amazing.
In X2: X-Men United, Mystique shapeshifts into a janitor to get in and out of a government facility with information on Magneto's prison guards. She employs Obfuscating Spanish when challenged. "Estoy echando la basura. Garbage." Leads to an amusing scene where she walks by the actual janitor, who's dumbfounded to see himself walking by (and is also an example of Making Use of the Twin).
Simon Templar does it in The Saint, seeking into the Big Bad's office disguised as a cleaning lady.
In Fist Of Fury, Bruce Lee's character, Chen, disguises himself as a telephone repairman to infiltrate the Japanese karate school.
The Fugitive (1993). Kimble dresses as a janitor to get into a hospital and use its computer system to locate the One Armed Man. Gerard lampshades it when he sees the phony ID card:
[with accent] "Desmondo, Jose Ruiz?"
Sneakers. Karl dresses as a gardener to get inside the Playtronics building by pretending to need to use their bathroom.
An especially interesting example in Monstrous Regiment, where Polly's regiment have to "disguise" themselves as washerwomen without revealing they're all really women. They are unconvincing as females.
Otherland: Olga Pirovsky infiltrates the tower of the J-Corporation disguised as a cleaning lady.
Happens frequently as part of the Zany Schemes in the works of P. G. Wodehouse. In Something Fresh, the first novel set at Blandings Castle, hero Ashe Marson and heroine Joan Valentine are on opposing missions to steal a prized scarab and disguise themselves as a valet and a ladies' maid, respectively.
In the Laundry Files novel The Fuller Memorandum, avoiding this sort of infiltration is one of the reasons that the Laundry cannot outsource their LAN rewiring, with the other reason being that having people unaware of the Masquerade build the system that you are going to use to fight Eldritch Abominations is a very bad idea. Ironically, the person that Bob explains this to turns out to be The Mole.
Harry Dresden in Fool Moon disguises himself as a janitor to get into the SI station where a ready-to-transform werewolf is being held under arrest. It helps that he has a sort of cheap invisibility potion that lets him pass beneath everyone's notice.
On Burn Notice Michael decided to pretend to be a weekend janitor so he could steal some high tech access codes. When that only got him so far, he added a drunken Wounded Gazelle Gambit to do the rest.
On Saved by the Bell, Screech dresses as a female janitor to get into the girls' locker room.
Daisy from Dead Like Me once dressed as a cleaning lady to reap someone in their hotel room.
Mr & Mrs Smith (1996). In the pilot episode Mr. Smith (Scott Bakula) dresses up as a janitor to infiltrate a target installation and acquire information.
Human Target: a group of bad guys infiltrate a museum dressed as maintenance staff, with Chance and Ames among them.
The title character in Chuck has on more than one occasion gotten by security by pretending that someone has called the Nerd Herd to fix a computer problem.
In "Eye of the Beholder", Ash gets a job on the cleaning crew at the museum so he can scope the place out as part of the team's plan to steal the Crown Jewels.
And Emma does it in "Eat Yourself Slender".
Rain does this in an episode of Naturally Sadie to get proof that a famous designer is stealing Margaret's designs.
The Leverage crew does this all the time—usually it's Eliot posing as a janitor, but Hardison and Parker have done it as well.
Bodie on The Wire does a Janitor Impersonation Exit from a juvenile detention facility.
A standard tactic on the Mission: Impossible television series. Commonly, one of the IMF members would get into the target's location, then fake some sort of utility outage. Other members of the team would then pose as repairmen or technicians arriving to fix the problem.
In the original Knight Rider, Michael Knight has to infiltrate an army base, so he bribes a food service worker to let him have his job for the day. The man says for double the money, Michael can be his cousin as well. This comes in handy when Michael gets detained, but the original guy verifies that Michael is indeed his cousin who was filling in for the day.
An old classic in Shadowrun. By the 2070s, most corps have become wise to it by reading the public SIN of anyone who enters the premises off-hours, requiring you to either Kill and Replace the regular janitor or have your decker hack the security.
Prototype: Alex Mercer. Canonically he only does this - literally consuming and assuming the form of a janitor - once, and hates himself for it.
One of the missions in Mafia II has you enter a mafia controlled hotel that is having a meeting of the head of a rival family but dressing up as cleaners. They clean up the blood of some unfortunate person while planting bombs.
In Nancy Drew: The White Wolf of Icicle Creek, Nancy Drew acts as the lodge's new cook and maid in order to investigate the lodge guests.
Used twice in the "Dead Man's Switch" campaign of Shadowrun Returns. The second time it happens, the player is maintaining the guise of cleaning up his or her, uh, mess (several gallons of security guard blood) from the night before.
The Bureau Raid mission Grand Theft Auto V has Michael infiltrating the FIB headquarters as a janitor if you chose the Covert option.
In the first Mega Man Battle Network game, Mr. Match infiltrates and sabotages a number of houses, including Lan's, by posing as a repairman sent to do preventative maintenance in light of the recent attacks. You know, his own.
Agent 47 tends to do this a lot in Hitman, though exactly how often is at the discretion of the player. Sometimes they leave extra uniforms lying out, and sometimes you have to kill them.
In the "Reality Television" arc of Schlock Mercenary, Lieutenant Ebniroth actually gets hired as a janitor for the building he's meant to infiltrate. Since they don't know the mercenaries are after them, he doesn't have to disguise his identity at all, even bragging about how his service qualifies him for the job.
Kim Possible had an episode with a government agent mentor who turned up as the janitor. Kim didn't want anything to do with him because she thought he was just the janitor. He thought she always knew what he really was because he never expected his Canadian Secret agent uniform to be mistaken for a janitor uniform. He even had to explain he wasn't wearing a disguise.
Centurions had an episode where the main villain had infiltrated the installation as a janitor. He also revealed that every janitor in the installation was part of his conspiracy.
The Simpsons: In one opening, they had to break into a museum to reach their couch. They wore several disguises through the way and one of them was janitor.
This is how real world ninja are supposed to have worked.
Even if they're not spies, servants can overhear a lot of juicy information from their employers. Both in real life and in fiction, this is often exploited in the form of highly-paid interviews with journalists or in tell-all books.