"The Principal and the Pauper" is the second episode of The Simpsons' ninth season. It first aired on the Fox network in the United States on September 28, 1997.In the episode, Seymour Skinner begins to celebrate his twentieth anniversary as principal of Springfield Elementary School, when a man arrives claiming that Skinner has assumed his identity. Principal Skinner admits that his real name is Armin Tamzarian, and that he had thought the true Seymour Skinner, a friend from the Army, had died in the Vietnam War. Armin leaves Springfield, but is later persuaded to return as principal.

"The Principal and the Pauper" was written by Ken Keeler and directed by Steven Dean Moore. It guest-starred Martin Sheen as the real Seymour Skinner. Although it aired during the show's ninth season, it was a holdover from season eight.

The episode is one of the most controversial episodes of The Simpsons. Many fans and critics reacted extremely negatively to the revelation that Principal Skinner, a recurring character since the first season who had undergone much character development, was an impostor. The episode has been criticized by series creator Matt Groening, and by Harry Shearer, who provides the voice of Principal Skinner.

"The Principal and the Pauper" was the last episode of The Simpsons written by Ken Keeler, who also pitched the original idea for the episode. Many fans believe the episode is based on the story of Martin Guerre or the 1993 film Sommersby. According to animation director Steve Moore, one of the working titles for the episode was "Skinnersby". However, Keeler has said he was inspired by the Tichborne Case of nineteenth-century England. The episode's official title is a reference to the book The Prince and the Pauper by Mark Twain.

Producers Bill Oakley and Josh Weinstein were excited about the episode because Principal Skinner was one of their favorite characters. The pair had already written the season five episode "Sweet Seymour Skinner's Baadasssss Song", which was an in-depth study of the character. Oakley said he and Weinstein "spent a month immersed in the mind of Seymour Skinner" to prepare that episode, and from that point forward, took every opportunity to "tinker with [Skinner's] personality and his backstory and his homelife".

Describing the real Seymour Skinner, Keeler remarked, "It would have been easy to make him a really horrible, nasty, dislikeable guy, but we didn't do that. We made him just not quite right, not quite Skinner, and a little bit off. Bill Oakley said the idea behind the character was that he "just lacked pizzazz" The producers selected Martin Sheen to voice the character because they admired his performance in Apocalypse Now and felt his voice would be appropriate for a Vietnam veteran.

Keeler borrowed the name Armin Tamzarian from a claims adjuster who had assisted him after a car accident when he moved to Los Angeles. However, the real Tamzarian (now a California Superior Court Judge) was unaware his name was being used until after the episode aired. Keeler said he later received a "curtly phrased" letter from Tamzarian, who wanted to know why his name appeared in the episode. Keeler feared he would face legal troubles, but afterwards, Tamzarian explained that he was simply curious and did not intend to scare anyone.