Pig-Pen is a fictional character in the comic strip Peanuts by Charles M. Schulz, syndicated in daily and Sunday newspapers in numerous countries all over the world.

Once, after bathing and dressing in clean clothes, Pig-Pen stepped outside his house and instantaneously became dirty and disheveled, whereupon he declared to Charlie Brown, "You know what I am?

On another occasion, Pig-Pen decided it was important to have clean hands, but after failing to wash them, realized that he had "reached a point of no return."

One notable exception is an earlier strip where he gets caught in a brief but heavy rainfall, and while trying to seek shelter, the storm ends, revealing him to be clean.

He may be carrying the soil that was trod upon by Solomon or Nebuchadnezzar or Genghis Khan!Charles Schulz admitted that he came to regret Pig-Pen's popularity, given the character's essentially one-joke nature; he utilized the character very rarely in the later years of the strip's run; Pig-Pen was featured in just over 100 of the 17,897 Peanuts comic strips that Schulz created (though still appearing commonly in the TV specials and movies of the franchise).

One time, his clean self was shown in a miniseries titled This Is America, Charlie Brown, where he is an astronaut aboard a futuristic space station, demonstrating how personal hygiene would apply in zero gravity.

In the 1990s, he appeared (in an animated overlay against a live-action backdrop) in a series of television commercials for Regina vacuum cleaners where all the dirt is sucked off his body and filthy trousers by one of the company's products, arguably one of the few times where Pig-Pen remains clean.