Captain Underpants is the superhero persona of Principal Benjamin "Benny" Krupp in the movie Captain Underpants: The First Epic Movie.
As Mr Krupp he wears a white shirt, green pants and a brown tie as well a brown small wig on top of his head. But when he becomes Captain Underpants he just wears his underwear and uses a curtain as a cape.
He is known to be the grouchy, mean, and cruel principal of Jerome Horwitz Elementary School, hating children for unknown reasons. But he mostly hates pranks, jokes and even smiles. It is mostly because he has been alone most of his life.
However as Captain Underpants he is on the opposite side, he is as he is nice and kind to everyone, especially children. But he is very dim-witted and at first he thought he did have superpowers.
Captain Underpants: The First Epic Movie
Mr. Krupp is bent on busting George and Harold of their multiple pranks they had done to him and the other staff, though he finds it upsetting that he hasn't gotten any evidence to have them punished. He also hates their Captain Underpants comics as he forbids them from creating any in the school grounds, even tearing up their latest one detailing the origins of the superhero.
George and Harold's pranks come to an apparent end after they tamper with a toilet invention called the Turbo Toilet 2000 made by the school's local snitch Melvin Sneedly. With that in mind, Krupp happily decides to place George and Harold in separate classes in order to annihilate their friendship and their pranks. But before Krupp could fill up the paperwork to make it happen, George hypnotizes Krupp with a 3D Hypno-Ring he received out of a cereal box; the boys see that Krupp bears a resemblance to Captain Underpants without his toupee and command him to be Captain Underpants. However, this quickly backfires when Captain Underpants begins causing some problems around Piqua, thinking he is a real superhero with superpowers.
The boys discover that they can turn Captain Underpants back into Krupp by splashing water on him and can turn him back 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. The boys even learn (after exploring his house) that Krupp might not be as evil as they thought, but has rather been lonely for most of his life.
During the fight against Tippy Tinkletrousers and the Turbo Toilet 2000, the boys change Krupp into Captain Underpants to help them fight off the villains. After consuming the rotten leftovers inside the dead Turbo Toilet 2000, Captain Underpants was able to obtain superpowers to finally defeat Poopypants, becoming a true hero to the public. However, George and Harold destroy the 3D Hypno-Ring in an attempt to permanently change him back into Krupp, as they knew that they can't control Captain Underpants. Feeling that Krupp would be nicer if he had friends, the boys set him and the lovesick Edith up on a date. This made Krupp have a change of heart, even returning the comics he took away from George and Harold, admitting that they 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 the talking toilets, which confuses George, as he thought destroying the ring would destroy the hypnotism.