Prince and Pauper

God bless the King--I mean the faith's defender;
God bless (no harm in blessing) the pretender;
But who pretender is, or who is King--
God bless us all--that's quite another thing.

—John Byrom

Prince and Pauper is a type of plot that is a combination of Swapped Roles, Identical Stranger, Princess for a Day and Fish Out of Water. Two physically identical people from different backgrounds swap roles (either by fate or by arrangement) and have to learn how to fake being each other. Everyone usually has An Aesop before episode's end.

Comes from the story The Prince and the Pauper by Mark Twain, and is regularly used in Disney TV movies, but not commonly in TV episodes (unless twins are involved).

If one is literally a prince (or other royalty), there will usually be a plot by an Evil Chancellor to depose them already underway when the switch happens.

Compare with Emergency Impersonation and Freaky Friday Flip. Also see Mock Millionaire.

Examples of Prince and Pauper include:

Anime and Manga

This happens in Turn A Gundam when the queen of the Moonrace decides to switch places with a lookalike on a whim. This has severe repercussions on both characters and on the war between the Moonrace and Earthrace, ultimately culminating in the lookalike becoming Queen of the Moonrace in the actual queen's place.
The Detective Conan/Lupin III crossover special twists this trope a little by having one of the parties (a bratty Rebellious Princess) trick the other (Ran Mouri from Conan) into swapping clothing, then runs off.
One Pokémon episode (shown in the page image) has Dawn trade places with a princess who wanted to participate in a Pokemon contest, who then gave her Togekiss to Dawn to gain experience as she traveled.
This happened ten years before the beginning of Princess Principal, with Princess Charlotte of Albion and her friend Ange taking each other's place on the day of a revolution that left them on opposite sides of a Berlin-style wall. For bonus irony points, "Ange" has become a spy in that time, and has been assigned to take the place of "Princess Charlotte", which leads to their reunion. At the same time, "Charlotte"—initially an illiterate street urchin—drove herself to excel in everything she needed to know to be a princess, simply for self-preservation.

Comic Books

In one Archie comic, Lil' Archie agrees to take the place of a weary prince who is identical to him. Lil Archie then successfully puts down an uprising, while the Prince is off enjoying his freedom.
Bunty, a British comic for girls, used this plot a few times. One recurring strip involved a wealthy Victorian heiress switching places with her maid for a day, but then the maid steals a valuable heirloom belonging to the heiress and claims to be her. The real heiress is forced to remain as a servant until she can find a way to prove her identity.
The 1987 UK Anthology Comic Nipper had a strip called "Will & Bill", in which a working class kid who looked identical to the then-five-year-old Prince William would exchange places with him.

Film

Trading Places plays with this; the people aren't physically identical. Instead, two really rich old guys are pulling the strings.
The various versions of The Parent Trap, including a movie starring the 11-year-old Olsen Twins, use a variant on this plot in which each of the swapped characters are both "prince" and "pauper" at the same time.
- And in all versions except the one with the Olsen Twins (which was titled It Takes Two), the protagonists were related. Incidentally, the only film versions to actually have twins playing twins were the original Das doppelte Lottchen, and the 1953 UK version Twice Upon A Time.
- One of the sequels to the 1961 Disney film cast a genuine set of triplets.
The Lizzie McGuire Movie had Lizzie swapping places with an Italian pop idol.
The Little Rascals short "Alfalfa's Double" has a rich kid named Cornelius from another neighborhood who looks just like Alfalfa. When he bumps into Alfalfa they decide to swap roles. Hilarity Ensues.
The Great Dictator, where Charlie Chaplin plays both a Hitler-esque dictator and a Jewish barber, naturally ends up like this.
Class Act has a juvenile delinquent and a genius high school student end up swapping roles when their pictures are swapped on their school records.

Literature

The trope is named for the Mark Twain novel The Prince and the Pauper in which Street Urchin Tom Canty gets mixed up with Prince Edward VI of England.
- An element that rarely get used in other works is that both try to come clean and get it reversed. Of course, even at the crowning ceremony no-one takes the pretender seriously that he isn't really the prince until the real one shows up.
Das doppelte Lottchen, published in English as Lottie and Lisa, is the original book that all the Parent Trap-style films are offshoot adaptations of.
Quoted, played straight, subverted, lampshaded, deconstructed, and reconstructed in Billy and Howard. Repeatedly.
This is the main plot element of Anthony Hope's 1894 novel The Prisoner of Zenda (and the subsequent film).
A similar plot is used by Robert Heinlein in Double Star, although to be fair the duplicate is an actor who uses his own skill at acting, rather than merely accidentally being a body double.
Parodied and subverted all to heck in Split Heirs by Lawrence Watt-Evans and Esther Friesner, in which there are three physically identical people (though one is a girl raised as a boy).
Happens in the Narnia book The Horse and His Boy with Shasta and Corin. It turns out that the "pauper" is actually the rightful prince, and the "prince" is just his few-minutes-younger identical twin. Said twin is happy to find this out because it means he doesn't have to bother with the responsibility of being king.
Happens in Myth Adventures novel Hit or Myth, where King Roderick convinces protagonist Skeeve, the court magician, to temporarily take his place using illusion magic. Of course, Skeeve finds out a little too late that the King did it because he was due to be married to the queen of a neighboring kingdom who's rumored to be insanely greedy and bloodthirsty. It turns out that the Queen IS ambitious and clever, but not evil, and catches on to the switch instantly... but when she shows more interest in marrying Skeeve than the King, the conflict becomes finding the King and getting him back to the wedding without the Queen finding out and killing him.

Live-Action TV

The premise of the Australian TV show Minty.
Used and spoofed in the Tripping the Rift episode "Nature vs. Nurture".
Happens in the Xena: Warrior Princess episode "Warrior... Princess", where Xena (a commoner, despite her nickname) temporarily switches places with an identical-looking princess at the local king's request.
In the third season The Man from U.N.C.L.E. episode "The Galatea Affair", U.N.C.L.E. agent Mark Slate is tasked with teaching working-class Bronx bar performer Rosie Shlagenheimer to act like THRUSH minion Baroness Bibi De Chasseur (both roles played by Joan Collins).
This concept is used in a Wishbone episode where he is telling the story.
The Monkees episode "The Prince and the Paupers", where Davy impersonates a prince to help him get married.

Music

In the 1896 John Philip Sousa opera "El Capitain," Don Enrico Medgua, the Viceroy of Peru, doubles for "El Capitain", the leader of the rebellion against the Spanish rule in Peru.
The Moxy Früvous song "King of Spain" is all about this:

"Prince and pauper
Junior and Whopper
World made up of
Silver and copper
Under my own volition
I took a change of position!"

Used in The Story of Evil: Rillianne, who was a terrible ruler, switches places with her servant and twin brother, Allen. A bit unusual in that this is not the beginning of the plot, but rather the dramatic climax of it and that Allen himself organizes the whole thing to save her from an upris1ing. Under the Princess' guise, he is captured and promptly decapitated while the Princess successfully escapes. In a later song, Rillianne is shown being burdened with regrets over his death, and in the finale she becomes a lowly nun in a monastery, so I guess An Aesop was learned as usual.

Newspaper Comics

Bloom County had Opus temporarily switch places with Michael Jackson at his request during MJ's heyday. Suprsingly, no one noticed.

Theater

The Zany Scheme subplot of The Taming of the Shrew, wherein Lucentio (son of a wealthy merchant from Pisa) and Tranio (his servant) switch clothes upon arriving in Padua. Tranio takes on Lucentio's identity while Lucentio pretends to be a tutor. (Whether the two actually resemble each other depends on your interpretation of the line "We have not yet been seen in any house/Nor can we be distinguished by our faces/For man or master". Regardless, it's clear that they get away with the switch because no one in Padua knows them, and in performance they generally look nothing alike.)

Western Animation

Used and spoofed in the Johnny Bravo cartoon "The Prince and the Pinhead", which had a cartoon version of Mark Twain show up near the end to complain about the overuse of this plot.

Johnny: Hey, you ain't one of them rich princes who wants to switch places with his exact double, are you?
Prince: Um, why, yes I am. You see, I -
Johnny: Wanna experience life as a commoner, I know.
Prince: Am I really that transparent?
Johnny: Naw, I just seen a lot of TV.

In the 1987 Teenage Mutant Ninja Turtles episode "April's Fool", Shredder kidnaps April after confusing her for a princess in order to get a jewel as ransom.
Done in The Simpsons, with Bart swapping places with a rich kid... whose siblings are trying to kill him.
Mickey Mouse starred in an adaption of the Twain story.
Candace did it in the Phineas and Ferb episode "Make Play".
The Veggie Tales video "Princess and the Popstar - A Story of Trading Places".
In an episode of The Hub's Pound Puppies series, team member Squirt and high society pooch Mr. Cuddlesworth switch places after meeting at the shelter when the latter chihuahua runs away from his home.
Open Season 3, where Boog the bear is accidentally mistaken for a Russian circus bear who looked exactly like him, while the real Russian bear simultaneously traded places with him so that he can live in the wild.
The Pink Panther and Sons episode "Millionaire Murfel" had Murfel trading places with a millionaire.
A Jem episode featured a princess who looked like Kimber.
The Proud Family has a forced switch between Mariah Carey's pet monkey and Oscar's Mr. Chips when Oscar, while distracted by Carey's presence at the vet's office, threw an injured Mr. Chips into a sick room that was already occupied by Carey's monkey (who was sick due to eating Proud Snacks). Things go uphill for Mr. Chips (who is mistaken by Carey for Mariah's), and downhill for her pet, with the latter experiencing something close to slave labor regarding meals, and later having its piano playing skills exploited for cash. Things end up back to normal after the pet finds Mr. Chips, takes back his identity forcefully, and both return to their rightful owners.
Done in an episode of Popeye & Son with Junior and a prince.
In an episode of Fish Hooks, Oscar gets mistaken for the Queen of Fish England when he impersonates her and almost ends up getting married to Mr. Muscles. At the end, the real Queen of Fish England shows up, and we find out that she was at Freshwater High impersonating Oscar... for some reason.