Skeleton Key

A skeleton key (also known as a pass key) is a master key often used by locksmiths, that will open any lock in the set of locks for which it is made. In fiction, a skeleton key will open any lock or Locked Door, period, and will often be shaped like a skeleton, skull or bone (partly a Sight Gag and partly a visual clue as to the key's purpose). More realistic examples have a full keyring of them, one for each type of lock.

Subtrope of Cool Key. Compare Interchangeable Antimatter Keys (which this is one step up from). Not the same as a Skeleton Key Card (which is just jimmying the lock with a piece of plastic). Not to be confused with The Skeleton Key.

Comics

 * Depictions of Batman's Utility Belt that listed its contents used to include a set of skeleton keys that could unlock 90% of known locks.
 * Thomson and Thompson use a ring of skeleton keys in several books.

Film

 * Beetlejuice had Lydia get a skeleton key from a relative of the deceased couple.
 * The Matrix Reloaded doesn't have a master key, it has the Key Maker, a living embodiment of this trope: a humanoid sentient program with the ability to produce a key that unlocks any door or lock that he comes across in the virtual world, including system backdoors.
 * In Harold and Maude, Maude carries a skeleton key that she uses to drive off in whatever vehicle she chooses. (At one point they ride off on a cop's motorcycle.)
 * The Skeleton Key naturally involves a skeleton key that will open any door in the mansion where the protagonist has taken a job.

Live Action TV

 * On Doctor Who, the Doctor's sonic screwdriver often acts as one of these.
 * In the episode, "Carnival of Monsters", the Doctor complains that he can't open a non-electronic lock with the sonic screwdriver. Jo Grant responds by producing an impressive collection of skeleton keys.
 * In The Wild Wild West, Jim West carried a skeleton key that seemed able to open almost any lock he encountered.
 * In the Scrubs episode "My Jerks," the Janitor is revealed to have made a key that works on everything. Said key is confiscated by Dr. Maddox.
 * The Price Is Right has a game called Master Key, where the contestant must select a key to see which prize it unlocks (if it unlocks anything at all). If they select the Master Key, all prizes will be unlocked.

Literature

 * The Last Apprentice: Tom and Mr. Gregory have skeleton keys provided by Gregory's brother, a locksmith.
 * In Scooby Doo! and the Skeleton Key, Scooby and the gang find an old-fashioned skeleton key - which the ghost of a pirate wants.
 * The Universal Castle Key in Septimus Heap.

Tabletop RPG

 * Dungeons & Dragons has had several magical keys that could open any lock, such as the Key of Opening, the Silver Key of Portals and Skeleton Keys (I and II).
 * Also worth noting is the spell Knock, which, when cast, immediately opens (or closes) most objects that can be opened (or closed): doors, chests, boxes, etc. If a door is barred by magic, Knock shuts the magic off for 10 minutes, and conventional locks simply unlock. Knock's only major limitation is that it only bypasses up to two mechanisms "preventing egress" per casting: a chest with a padlock, a numbered combination lock, and a magical seal keyed to its owner will take two casts of Knock to open. Amusingly, Knock can be keyed to a Wand for repeated casting, effectively making the person holding the wand (presumably a Wizard) better at unlocking things than characters who specialize in lockpicking.
 * Shadowrun has several devices that can bypass electronic locks.
 * A maglock passkey can be used to open any maglock (magnetic lock) door. The higher the passkey's rating, the more likely it can open the lock.
 * The Neo-Anarchists' Guide to Real Life has devices that can do the same thing with keypads and cardreaders. The keypad sequencer feeds a keypad system a series of passcodes, and a passcard (AKA skeleton card) does the same with the cardreader it's inserted into.
 * The "Skeleton Key" is a character template in BESM Third Edition; they have the power to open the portals between worlds, and have the Dynamic Power (low-level, though) to open locks both physical and metaphysical, making them quite sought after by those who know of them. There's also a BESM artifact called the Janitor's Key Ring which can open any lock if the user simply tries enough keys from the key ring.

Theater

 * In the song, "With Cat-like Tread" from The Pirates of Penzance, one of the pirates' tools are their "skeletonic keys."

Video Games

 * Alyx Vance appears to have an electronic one about half-way through Half Life 2, which opens all doors in Nova Prospekt and can also hack Combine computer consoles.
 * Subversion: In World of Warcraft, the key to open the Scholomance door is called the Skeleton Key and has a skull-shaped bow, but otherwise is apparently just a normal key that opens one particular door.
 * Played straight, however, with the Skeleton Keys made by Blacksmiths which will open any lock up to a particular difficulty.
 * The Skeleton Key artifact, an unbreakable lockpick that fortifies your "security" skill, has appeared in every main game of The Elder Scrolls series so far, as an artifact primarily associated with the Daedric Prince Nocturnal:
 * In Arena, it is obtained in Valenwood or Sommerset that opens any non-magical lock once a day.
 * In Daggerfall, it is similar to the Arena version but can now open weak magic locks and also be worn as amulet for stats boost. It is obtained directly from Nocturnal by summoning her on a certain day.
 * In Morrowind, the Skeleton Key is given to you at the end of the Thieves Guild storyline. However, this time it isn't an artifact but a regular lockpick that has very, very good stats but only 50 uses.
 * In Oblivion you get a Skeleton Key as a reward for completing a side-quest for a statue of Nocturnal. In this case, the Skeleton Key is an unbreakable lockpick that greatly increases your lockpick skill; this allows players to simply press the button to automatically make an attempt over and over until the lock opens, allowing for any pickable locks to be bypassed entirely.
 * The Skeleton Key takes a level in badass story-wise in Skyrim. It can open any door, even doors that require multiple keys or puzzles to solve, doors that don't even have keyholes, In-game it's "just" an unbreakable lockpick. Unfortunately, to finish the Thieves' Guild questline you have to return it to Nocturnal.
 * In Excelsior Phase One: Lysandia, these are used to pick locks, instead of normal lockpicks.
 * The Keyblades of Kingdom Hearts fame can open or close any lock as one of their many abilities. True, it does this with a magical bolt of light, but it still counts, right?
 * Mario Party 2 and 3 have Skeleton Keys
 * Zelda generally relies on Interchangeable Antimatter Keys, but in the SNES The Legend of Zelda a Link To T He Past, the "Big Key" was the only key that could be used several times in the dungeon (it only opened big locks, though).
 * In later games, the Big Key only unlocked the entrance to the boss's lair, and was sometimes called the Boss Key for this reason.
 * In The Legend of Zelda the Minish Cap, though, the Big Key in the Palace of Winds is used to open two doors, one of which is halfway through the dungeon.
 * The first two Zelda games both had a key item that basically served as infinite keys for the remainder of the game. The sixth palace in Zelda II the Adventure of Link couldn't be beaten without it.
 * The first The Legend of Zelda game had a Magic Key by the 8th dungeon that acted as a infinite use key, being able to open all locks without wasting the key like normal keys.
 * One shows up in King's Quest VI—it not only opens any lock (which is useful in case Alex gets imprisoned), it's also shaped like a skeleton, and Alex has to steal it from a real skeleton.
 * Nethack has both a Skeleton Key and a Skeleton Key Card.
 * Kingdom of Loathing has a skeleton key that, like the page image, has skeleton imagery on it. It avoids being overpowered by snapping every once and a while.
 * It also has the same Skeleton Key Card from Nethack as a Shout-Out. This one doesn't break, because it's an incredibly rare and valuable item to begin with.
 * In Deadly Premonition, York is given a master key for every police car in Greenvale.
 * In the adventure game The Last Express you can obtain a key that opens all the locks on the train, belonging to the conductor, and you can use it to sneak into other people's compartments and snoop around for information.
 * Task Maker has Skeleton Keys that open any locked door. Its sequel, The Tomb of the TaskMaker, also has lock picks which can be used if the player is a Thief.
 * Dragon Quest III has three different skeleton keys, with the final incarnation being able to open any door. Or you could just use that spell.
 * Castlevania: Harmony of Dissonance features a Lure Key that opens almost all the doors in the castle, to ease backtracking in the later parts of the game. There are two doors that it doesn't work on - MK's Bracelet opens one, and the Skull Key opens the other.
 * In Ultima V, the player can acquire Skull Keys which effortlessly open magically locked doors. (Oddly, since they can all be unlocked by the "Unlock Magic" spell anyway, magical doors are notably *less* secure than normally locked doors.)
 * The Binding of Isaac has one of these as a random power. It's the only Interchangeable Antimatter Key which isn't made of antimatter, so it sets your key count to the cap of 99.
 * The Master Key, one of the starting gifts in Dark Souls, can open several non-progression related doors that would otherwise require other keys to open.
 * Using the  cheat code on Doom gives the player (amongst other goodies) skeleton keys instead of the regular keycards, but these aren't Interchangeable Antimatter Keys either (other than losing them at the end of each level). In Doom2 there are doors that can only be opened by these skeleton keys, but then they can obtained by means other than cheating.
 * Pokémon has several of these. In Pokémon Red and Blue and Yellow, there was a key card that, once obtained, unlocked all the doors in the Rocket Hideout. A similar key must be obtained in Pokémon Diamond and Pearl and Platinum to unlock all the doors at the Team Galactic building in Veilstone City.

Western Animation

 * In The Simpsons, Chief Wiggum has a police master key that opens any door in Springfield. Bart and Ralph steal at and get up to mayhem.
 * The Fairly OddParents: Cosmo mentions in one episode that he once had a terrible job as a magic key, implied to be one of a skeleton nature.
 * In Danny Phantom, The Skeleton Key is a ghostly artifact that Vlad seeks out in The Million Dollar Ghost, and eventually leads to the events in Reign Storm when he uses it to release Pariah Dark.

Web Original

 * The SCP Foundation has this, it is called SCP-005.

Real Life

 * Security guards will often have either a giant keyring or a single key designed to operate every door in a specific area.
 * As will janitors, maintenance people, housekeeping, etc.