Dr. Diaper is a villain from the Captain Underpants novels. He is the main antagonist of the first book. His plan to destroy the moon with the Lazer Matic 2000 and all the big hunks of it would come crashing down on Earth, destroying every major city. This chaos would allow him to take over the planet. His plan was foiled by George, Harold, and Captain Underpants and he went to jail.
- He is the only Captain Underpants antagonist lacking an origin.
- Dr. Diaper makes a cameo in The Perilous Plot of Professor Poopypants as one of the inmates laughing at the title character.