10. The REAL Seymour Skinner
In 1997's season 9 episode 'Principal and the Pauper', it is revealed that principal Skinner is an impostor by the name of 'Armin Tamzarian', and had taken on the role of 'the real Seymour Skinner', a US Army Sergeant who went missing in action, presumed dead. When the real Skinner turns up, however, Armin's elaborate ruse is exposed as Seymour takes his life back, including becoming Springfield Elementary's new principal and moving back in with his mother, leaving Armin out in the cold. Fortunately, nobody likes the real Seymour (indeed, viewers consider this to be one of the worst Simpsons episodes ever made) and he is eventually ran out of town, with Judge Snyder ruling that no one will mention "Tamzarian" again under penalty of torture, as "Seymour Skinner" gets his old life back as though nothing had happened.