George and Harold are best friends with that have almost everything in common, right up to the fact that they live right next door and go to the same fourth-grade classes. George and Harold cannot help themselves when it comes to practical jokes. In every book, they change the letters on a sign to something funny or rude.
Their teachers usually describe them to be "behaviorally challenged", disruptive, and in serious need for an "attitude adjustment". Principal Krupp often describes them as "sneaky", "criminally mischievous", and often vows that he will "get those two if it's the last thing he does". They make their own comic books that they sell to people at school for 50 cents. In the first book, they hypnotize Mr. Krupp to believe he is a superhero from one of their comics, Captain Underpants. Due to that, they had to save the world, even when someone snaps his fingers! He has five pet goldfish named Moe, Larry, Curly, Dr. Howard, and Superfang.