On the occassion of
Principal Seymour Skinner's twentieth anniversary at
Springfield Elementary School the faculty and children held a surprise tribute to Skinner one evening in 1997. During the festivities, however, an
army sargeant burst into the auditorium and proclaimed that he was the real
Seymour Skinner and the Skinner we all know and love as principal in
The Simpsons universe was an imposter. "Our"
Skinner confessed that he was actually Armin Tanzarian, a nogoodnik from
Capital City. After spending his teen years snatching purses and causing trouble, he was sentenced to the
army where the real Skinner took him under his wing.
After his mentor was presumed killed in action, Armin returned to Springfield to break the horrible news to Skinner's mother, Agnes. Instead of telling her the news, however, he claimed to be Skinner and summarily assumed the sargeant's old life and aspirations. "I don't know why I did what I did," Armin said of his actions when exposed. "I guess I couldn't bear to tell her about her son. What I did was wrong, but... I'd do it again."
After being exposed Armin left town in shame. The real Seymour Skinner took over as principal of the elementary school, and that could have been the end of the matter. Instead, as time passed, the people of Springfield came to realize that they didn't like the real Skinner; they liked the one they've known for the past 20+ years. Homer Simpson and his family plus faux-mother Agnes Skinner and girlfriend Edna Krabapple traveled to Capital City to find Armin and convince him to return to Springfield. In the end the townspeople ran the real Skinner out of town on a rail and Judge Snyder confered upon Armin the name of Seymour Skinner, as well as his past, present, future, and mother. Furthermore he decreed that "everything will be just like it was before all this happened, and no one will ever mention it again... under penalty of torture."
And so it came to pass that Armin (um, I mean Seymour) was reinstated as principal and nobody on the series has ever spoken of the incident again. In fact, there have been only two mentions of the Tanzarian matter: a futuristic dream sequence in a later episode featured a tombstone in the background of a cemetary scene marked "Tanzarian" and Lisa Simpson's referral to the principal as an example of a deus ex machina.
References:
http://www.snpp.com/episodes/4F23