<Li> George R. Beard: one of the main protagonists and a 4th grader at Jerome Horwitz Elementary School . Harold's best friend . </Li> <Li> Harold M. Hutchins: one of the main protagonists and a 4th grader at Jerome Horwitz Elementary School . George's best friend . </Li> <Li> Mr. Krupp: Jerome Horwitz Elementary School's cruel principal who hates George and Harold . </Li> <Li> The Amazing Captain Underpants: A super hero from George and Harold's comics, George and Harold accidentally hypnotize Mr. Krupp into thinking he's Captain Underpants . </Li>

What is the main idea of captain underpants