Plot

Two overly-imaginative pranksters hypnotize their grumpy principal into thinking he's a ridiculously enthusiastic, incredibly dimwitted, underwear-themed superhero.

George and Harold are two imaginative pranksters who make the depressing Jerome Horwitz School a better place. They hypnotize their nemesis, the mean-spirited principal Mr. Krupp. He transforms into the incredibly clueless yet kind-hearted and enthusiastic superhero named Captain Underpants. Even without the mean principal, they discover that having Captain Underpants comes at a steep price. Meanwhile, Professor Poopypants tries to eliminate laughter with the school snitch Melvin, and George and Harold discover that there may be more to Mr. Krupp than they had originally thought.—Ken

In the city of Piqua, Ohio, two fourth-grade friends and next-door neighbors named George Beard (Kevin Hart) and Harold Hutchins (Thomas Middleditch) are the pranksters at their school, Jerome Horwitz Elementary School. They excessively pull numerous pranks on the cruel teachers, many of which are directed at their mean-spirited principal, Benjamin Krupp (Ed Helms), putting the two at odds with him. The duo also create comic books about a superhero named Captain Underpants, who fights crime while wearing underwear and a cape. They distribute these to their schoolmates through a comic company called Treehouse Comix Inc., located in their tree-house. George and Harold's pranks come to an apparent end after they're caught tampering with a toilet invention, the Turbo Toilet 2000, made by the school's local snitch and intellectual, Melvin Sneedly (Jordan Peele), on video with Melvin's tattle-turtle. Finally having solid proof of the boys' antics, Mr. Krupp excitedly prepares to annihilate their friendship by putting them in separate classes..

Based on the bestselling book series, DreamWorks Animation presents the long-awaited global movie event, Captain Underpants. This outrageous family comedy tells the story of two overly imaginative pranksters, George (Kevin Hart) and Harold (Thomas Middleditch), who hypnotize their principal (Ed Helms) into thinking he's an enthusiastic, yet dimwitted, superhero named Captain Underpants.—20th Century Fox

Two young males team up with their school principal to go out into the streets of their town to fight crime as a vigilante team. Things go bad and wrong when they stumble onto a real evil plot to take over the town and everyone who lives in the town.—RECB3

In the town of Piqua, Ohio, two fourth-grade friends and next-door neighbors named George Beard (Kevin Hart) and Harold Hutchins (Thomas Middleditch) are the pranksters at their school, Jerome Horwitz Elementary School.

They excessively prank the cruel teachers, with many of these pranks directed at their "evil" principal, Benjamin "Benny" Krupp (Ed Helms), putting the two at odds with him. The duo also creates comic books about a superhero named Captain Underpants, a character who has superpowers and wears underwear and a cape. They sell these to their schoolmates through a comic company called Treehouse Comix Inc., located in their tree-house. Harold loves to draw, and George loves to tell stories. Krupp is livid when George and Harold make comic books during their time at school and had confiscated make of their original comic books in the past. Krupp hates anything fun.

George and Harold are responsible for innumerable pranks on the school campus, most of them aimed at infuriating Krupp. Krupp is only looking for some solid proof to get rid of the duo. Krupp announces an invention convention at school at 8 am on the coming Saturday. Kids are livid as this is the 3rd Saturday in a month that Krupp has summoned them to school.

George and Harold's pranks come to an apparent end after they tamper with a toilet invention, the Turbo Toilet 2000, made by the school's local snitch and intellectual, Melvin Sneedley (Jordan Peele). Melvin brought 17 inventions to the convention was boring the school, which is why George and Harold took action. This causes Krupp to decide to separate the boys into different classes and annihilate their friendship when Melvin presents a video clearly showing the prank being performed by George and Harold.

George and Harold know that being in separate classes will lead to separate lives and soon they fear that they will be nodding at each other in the mall. They both decide to get the nanny cam which was used to Melvin to spy on them. While going through Krupp's drawers, the boys find everything that Krupp ever confiscated from them, including a 3D Hyno ring.

To prevent this, George hypnotizes Krupp with a 3D Hypno Ring he received out of a cereal box. The boys see that Krupp bears an odd resemblance to Captain Underpants without his toupee and command him to be Captain Underpants. The boys soon learn the severity of their actions when "Captain Underpants" begins causing problems around Piqua. Captain underpants punches a mime (as he could not hear him), throws an old lady into a tree (who was trying to rescue her cat), and battles a giant balloon gorilla, by jumping on it from the top of a tall building. The boys try to rescue Underpants with a crane, but he ends up falling on top of 2 thieves who try to rob a bank, thereby cementing his superhero image in his own mind.

To prevent these issues, the boys take him to their tree-house, where they discover that they can turn Captain Underpants back into Krupp by splashing water on him and can turn him back into Captain Underpants by snapping their fingers. Believing that Krupp will continue with his plan to separate them, they decide to settle with Captain Underpants but insist that he be dressed up as Krupp under the pretense of a "secret identity," to which Captain Underpants agrees. His sudden personality change even manages to attract the attention (and affection) of the school's shy lunch lady, Edith (Kristen Schaal). George and Harold take Underpants to Krupp's home and find that Krupp leads a very lonely life. He has no friends and no companionship of any kind.

Just when George and Harold believe that their troubles have ended, Jerome Horwitz Elementary School is visited by an odd, German-accented scientist named Professor Pippy P. Poopypants (Nick Kroll), or as he calls himself, Professor P.

Captain Underpants (disguised as Krupp) hires him to be a new teacher, but George and Harold are suspicious of him. Poopypants, who invented a Nobel Prize-winning "Sizerator", is sick of never being taken seriously due to his name, and seeks to eliminate all laughter. With Captain Underpants as principal, the school becomes a livelier place, but a rainstorm turns Captain Underpants back into Mr. Krupp, who officially places George and Harold in separate classes.

Professor Poopypants tries to take over the town with a giant version of the Turbo Toilet 2000, fueled by the school cafeteria's rotten leftovers left out by Edith and uses Melvin's brain to turn the children into glum, humorless zombies. Captain Underpants tries to stop the villain, but due to having no actual superpowers, is effortlessly defeated and thrown into the toilet. George and Harold are captured and nearly turned into zombies but are able to escape when their laughter damages the Turbo Toilet 2000's computer, restoring the children back to normal. Upon consuming the mutated leftovers, Captain Underpants acquires superpowers and, with George and Harold's help, defeats and shrinks Poopypants, though he escapes shortly thereafter.

Knowing that they can't control Captain Underpants, George and Harold destroy the Hypno Ring to permanently change him back into Krupp. Feeling that Krupp would be nicer if he had friends, the boys set him and lovesick Edith up on a date, thus making Krupp have a change of heart, returns the comics he took away from George and Harold, and even admits their comics are funny. However, the toxic waste from the Turbo Toilet 2000 transforms all the toilets into vicious monsters which attack the restaurant at which Mr. Krupp and Edith are dining. Upon snapping his fingers (accidentally), Mr. Krupp once again becomes Captain Underpants, carrying George and Harold away to help him fight them, much to Edith's surprise and admiration.

George and Harold realize that the secretary, who they put on the phone before by faking a contest with a cash prize of $2 billion, has been on the phone for the entire film, so they shut off the call, make the secretary angry, and make a new comic based on her reaction.