Sometimes, a Game Master doesn't have enough players to run a decent game. Or else, he just wants to have his cake and eat it too. Or perhaps the campaign needs a Mr. Exposition and the rest of the party doesn't fit the bill. Either way, he starts out an important NPC to travel with the party and fill any missing roles no one else wants to play. It's almost like the GM has a Player Character of his own, thus this concept has come to be known as the GMPC.
Admittedly, this kind of character can be done well — adding flavor to the campaign and immersing the players in the world the Game Master has set out to create. This kind of GMPC often serves as a Non-Action Guy in order to avoid stealing the spotlight from the players, or at least some form of White Mage (passive GMPCs often end up in the 'healing' role).
However, it's all too easy to screw up the GMPC, especially since the Game Master also controls the game world and plot. Thus, the GMPC has a tendency to turn into a plot device to keep the players on track, stopping them from going Off the Rails. Even worse, the GM can take too much of a liking to his PC, and the character slowly but surely turns into a Mary Sue: defeating all the enemies singlehandedly, doing all the cool stuff, and gradually reducing the players to supporting roles. He might also set up the adventure to suit his character, without considering the others.
This kind of GMPC quickly earns the ire of the players, since what's the point of even playing the game if all the DM's going to do is play with himself? They came to the gaming table to play as fantastic characters, crack some heads, and have fun; not sit and watch some Marty Stu kick werewolves through buses (and in the case of the Munchkin, he wants to be the one kicking the werewolves through buses). This may lead them to try to kill the offending character, which inevitably fails because of countermeasures including unstealable Rings of Invincibility and hostile allies getting struck by 10d100 lightning bolts. The Game Master may quickly find himself without a game if he doesn't get a clue.
An equally problematic variant is the GMPC who is obnoxious, absolutely useless or worse. These characters exist mainly to cause trouble for the players through their sheer incompetence, yet they are too pivotal to the plot and/or the fate of the world for the PCs to leave them to their justly deserved fate. This has all the problems of an Escort Mission in a video game, compounded by the fact that the Dungeon Master is doing it intentionally, rather than because of the inferior AI of a game.
It should be noted that any campaign setting that contains significant canon NPCs (such as the Forgotten Realms) may fall victim to this if the GM insists on having them travel with the party. Just as bad is the habit of using them as a Deus ex Machina to bail out the party when they screw up, especially if you set up the PCs to fail on purpose.
There is a middle ground, a GMPC who behaves pretty much the same as most player characters, but you don't seem to hear much about them. Presumably because they don't make as exciting stories. A GMPC may be employed temporarily to stop new players from killing themselves before they've learned. It can also occur legitimately in a campaign where the role of GM rotates among the players.
(It should be noted though, in general, a GMPC in any game isn't going to solve any issues, come up with ideas, or take charge of any plot important situation the GM has set up for the player to do (unless he's not a very good GM prone to Rail Roading). Normally, this is fine when they're just an equal to you mook; this can get comical and bizarre if the GMPC is supposed to be your superior and/or a wizened, experienced character and the GM needs them to be incompetent, silent, or magically not available during crucial moments meant to be handled by the PC.)
Not to be confused with Gnome Music Player Client.
Examples of Tabletop Games requiring GMPCs:
- Bliss Stage's Authority Figure is one of these. Notable as one of the possible results of getting to 108 points of Bliss is for a Pilot to mutiny and take over La Résistance: If this happens, that pilot's player must become the new GM!
- In Fellowship, the Game Master plays the Overlord, a character that serves as the Big Bad of the campaign. It's the Fellowship's job to fight their armies and thwart their evil plans.
- My Life with Master in a nutshell: The PC's in this game are the Igors to the Game Master's Dr. Frankenstein GMPC.
- Maid RPG is a sendup of the entire Meido trope in which the GMPC "Master" can have a powerful artifact known as the Desu Note. ...Do I really need to say it? The players' effectiveness depends on seeking out (or contending for) the Master's approval. On the other hand, the way the rules are set up, Masters tend to be pretty helpless in everyday situations (for the game's definition of "everyday"), and players usually have an explicit power to randomly derail plots they don't like, so it balances out: even the author's self-insert GMPC gets accidentally killed by his maids. Twice.
- The Wild Card in Meddling Kids, a table-top game for kids based very loosely on mystery shows of the Scooby-Doo kind.
- Ninja Burger has the dispatcher, a Non-Action Guy. His job is to watch the PCs on closed circuit camera and basically provide them with hints and assistance as needed.
- Not a requirement, but Don't Rest Your Head has an optional rule where there is no assigned GM, and whoever gets the best roll in a scene gets to control the story, essentially making them the owner of a GMPC for a short time. You would expect this to cause problems, but considering the crowd that game draws in, it actually makes things quite interesting.
- The Ringworld RPG requires players whose characters mutate into protectors to give up control of the character to the GM. Protectors have superhuman strength and intelligence, but no free will, as they are ruthlessly devoted to ensuring the survival of their bloodline or species.
- Paranoia often saddles the players with an 'escort' that is this trope Played for Laughs. The opportunity to kill an obnoxiously perfect and completely unwanted NPC is one of the few things that will cause Paranoia characters to cooperate.
Non-Tabletop Game Examples:
- Dark Bakura from the Yu-Gi-Oh! manga is a literal Killer Game Master that frequently uses his own Player Characters to go against the players in his Tabletop RPG campaigns. In the first RPG, Dark Bakura is in control of a Big Bad Evil Guy and Ryou Bakura (the good one) manages to save Yugi and his friends from it using his own GMPC. In the second RPG, Dark Bakura is in control of two, Thief King Bakura and Priest Akhenaden. When Thief King Bakura dies, Akhenaden manages to summon Zorc Necrophades, and the demon replaces the thief as one of Dark Bakura's avatars.
- In Sword Art Online:
- A major plot twist is that Kayaba Akihiko, the Big Bad who trapped everyone in The Most Dangerous Video Game, was actually Heathcliff, leader of the Knights of the Blood guild. Kirito, having wondered where Kayaba had been for the last two years of the game, partially deduced his identity when he realized Heathcliff was in too good a condition after what should have been an exhausting battle for even a high-level player. The other key realization was, as Kirito put it, "Something any kid knows. There's nothing as boring as watching someone else play an RPG." It also turns out that he didn't even need those privileges in the first place, since he was the one who made the combat system in the first place and thus had the skill to match and beat Kirito in a straight-up duel without admin status.
- In the second arc, Fairy Dance, Sugou Nobuyuki creates an in-game avatar called Oberon, the Fairy King, just to further cement his arrogance and self-importance over everyone and in the Alternate Continuity Infinity Moment/Hollow Fragment creates a super-powerful avatar named Alberich to help him keep the players from completing the death game so he can use them for his Mind Control experiments. He proceeds to abuse his admin privileges for all their worth to torture Kirito and all of Asuna's friends as well in the latter solely to Kick the Dog. Of course, unlike Kayaba, he's pathetically weak combat-wise and once the heroes remove his Game Master privileges thanks to Kayaba's virtual ghost in the novels/anime and Strea in the games, they proceed to show him just how pathetic and outclassed he really is.
- Cait Sith, in Off the Line, is not only an NPC, but the game's admin, head designer and avatar of the game's creator. He also adds and changes things as long as he helping the player or if it amuses him.
- In Ponies and Dragons, Doctor Whooves had one (a Time Lord, too) when he ran the game. After Vinyl Scratch stabbed the character to death, shoved the body into a magic bag, and dumped it down a well, he took the hint and abdicated the GM seat. Vinyl still occasionally gives him grief for it, though.
- The Gamers: Dorkness Rising: Sir Osric is a Paladin and therefore honour-bound to curb the PCs' amoral-to-homicidal impulses, which causes resentment among the players (and characters) for the "babysitter". Ultimately a Reconstruction as the GM learns to have more faith in his players and develops Sir Osric's personality accordingly, while the players become more invested in the story and slightly less prone to hijinks. Ultimately, one player character uses her divinely-granted wish to bring Osric back from the dead — a major milestone in roleplaying for the group.
- In The Gamers: Natural One (with some of the same players) a different DM plays a combat character just to fill a hole in the group. He eventually ends up taking on a group of mooks solo while the players take on the adventure boss, but gets so distracted by it that they have to ask him to stop "playing with himself" and get back to the main fight.
- Kamen Rider Ex-Aid has Kuroto Dan/Kamen Rider Gemn, owner of the video game company that created the Riders' transformation belts and Gashats. Kuroto outright calls himself the Game Master, but rather than sitting on the sidelines, he transforms into a Rider and uses his complete knowledge of the Gashats (as well as his ability to create new ones when he wants) to completely dominate the heroes and serve as the show's Disc-One Final Boss. Tropes Are Not Bad in this case, since Kuroto ends up getting dethroned by unexpected surprises, undergoes a HeelFace Turn, and gets some Character Development that makes him interesting and sympathetic...that, and the fact that his actor Tetsuya Iwanaga was hammier than a hog farm and clearly had a lot of fun playing the character.
- Several in the Binder of Shame. For example, in "Achy Breaky Mythos," the GM had the players all play academics who had a "mutual friend," the adventurer Dick Marvil. The page quote came after Dick Marvil casually snapped the necks of nightgaunts who the PCs couldn't even scratch.
- In Red Dragon (the Role-Playing-Fiction on which Chaos Dragon was loosely based), Kinoko Nasu's airheaded paladin Swallow was accompanied at all times by his snarky maid Meryll, to whom he owed a great personal debt. Nasu created Meryll mostly to give the GM an easy way to stop him from going Off the Rails and stealing spotlight from the less experienced players, but due to a series of odd die rolls this soon lead to a Running Gag of the players treating her as the strongest member of the party while ignoring all of Swallow's accomplishments.
- In the D&D-themed Borderlands 2 DLC Tiny Tina's Assault on Dragon Keep, White Knight Roland serves this role, often appearing in the story just because Tina says so. The other players aren't very happy about this, partly because he's more or less a plot device and because he's a clear sign that Tina is in denial of the real Roland's death. However, the ending shows that his character is meant to be a tribute to Roland, ultimately having a better fate than his ignoble death at the hands of Handsome Jack.
- DM of the Rings is a Lord of the Rings-based Campaign Comic where a put-upon, railroading DM uses Gandalf the Grey as a DMPC. Antics include stealing the spotlight from the PCs with long-winded speeches and contrived heroics, trying with intermittent success to prevent said PCs from going Off the Rails, and rising from death with game-breaking new superpowers after the PCs abandoned him to a boss fight they didn't want to bother with.
- When the Hobbit players get fed up with the GM and leave, he responds by secretly taking over their characters and playing them in the background while the remaining players arent looking, getting Frodo and Sam to Mount Doom. The final battle ends up coming down to a single will-save for a GMPC whos not even in be scene. The players are not amused when they find out.
- The Noob has the MMORPG version, in which the Jerkass head developer plays a character. And cheats to try and win contests.
- Darths & Droids is a Star Wars Campaign Comic that uses this trope when the the regular GM can't make it to the session: Pete takes over as GM while still playing his PC R2-D2. During the battle, he decides R2-D2 has rocket thrusters, which in the movie, pretty much allows Artoo to save the day.
- The adaptation of A New Hope gives the regular GM his first chance at playing a party member: Chewbacca. After the death of Obi-Wan, the role of Chewbacca is passed to Ben.
- The regular GM later tries his hand at this during the Rogue One campaign, with decidedly mixed results. He does a decent job as Bodhi Rook, but his version of Jyn Erso is such an obnoxious load that the party barely tolerates her.
- In One Piece: Grand Line 3.5, it's revealed near the end of the Syrup Village arc that the GM designed one back when the group consisted of just Luke and Cory. Their old GM DM is surprised when she learns this, as she knows Cory especially hates GMPCs. He later end up having Sanji as a GMPC, but subvert it as of now, since Luke have been the one controlling Sanji in battle.
- Spoofed in this Penny Arcade comic, where Gabe is shown indulging in this during a Star Wars RPG.
- Steven and the Crystal GMs: Rose Quartz was Bettys GMPC in the games previous incarnation, making her treatment as the beloved Greater-Scope Paragon in the current game feel a little self-aggrandizing.
- While not quite a fit in this section, the MSF High Forum has a few of these. Mitchell, current head GM, is known for trying to make sure his stay out of the fight, especially at climaxes. For instance, Michelle was busy fighting her evil twin in an ultimately irrelevant battle (And lost), and includes one in his planned Mahou Galaxy adventure, and Legion-based online game.
- Fallout Is Dragons has a number of GMPCs, two of which are actually party members. They are actually about equal to the player characters and somewhat adored by the players themselves, although only Aurelia has actual stats.
- Mostly averted in Critical Role, but DM Matthew Mercer will occasionally control an allied NPC (or an absent player character) in certain battles if the story works out that way. Matt also has an infamous story about why he became a Dungeon Master, and it mostly boils down to his previous DM abusing his GMPC's privileges.
- Alan Sells, the GM of Pokémon World Tour: United, utilizes a GMPC in the form of Victor, a boy a few years younger than Rose and Cobalt who joins them early in their journey. For the most part, he's comic relief and his Lillipup, Biscuit, is a Ridiculously Cute Critter who helps lighten the mood as needed. When needed, however, Alan utilizes Victor to draw Rose's and Cobalt's players, Jake and Josh, towards potential plot points and keep various tangents from going too far.