Captain Underpants Wiki
For information about Old Benjamin Krupp's hero form, see Old Captain Underpants.

You know, it's hard to believe that you guys used to be the craziest kids in this school! Thank goodness you both started taking life seriously!
  —Old Mr. Krupp [src]  

Old Benjamin Krupp is the thirty-year-older version of Benjamin Krupp. He is voiced by Len Forgione in the Sound-O-Rama Audiobooks.


Captain Underpants and the Revolting Revenge of the Radioactive Robo-Boxers[]

When Old Mr. Krupp arrives and tells the teachers to get the students into class, George and Harold discover that the screaming teachers are themselves in the future. It is revealed by the adult George and Harold that the vow present-day George and Harold made on focusing more in class and start acting like adults is what caused them to become greatly similar to the teachers they were used to.

Immediately, George and Harold make a new vow to undo their previous vow and promise to always be themselves. As a result of this, the adult George and Harold disappear and it is unknown if they still exist in the future (albeit with different personalities). George and Harold snap Old Mr. Krupp into Old Captain Underpants to save younger Mr. Krupp (dressed as Captain Underpants) from being beaten up by Slightly Younger Tiny Tippy.