Mr. Ree is the school janitor and a former member of T.E.R.D.S. introduced in The Epic Tales of Captain Underpants. His name is a pun on "Mystery", while his full name is one on "Toiletry".
Mr. Ree originally was hired by the government to make T.E.R.D.S (toilet eliminator of really dangerous stuff) in the late 1990's. However, during the first official test flush, the handle got stuck, resulting in a massive flood, injuring and possibly killing many. They were shut down and Mr. Ree abandoned T.E.R.D.S in his past.
He later became a janitor at Jerome Horwitz Elementary School, and with George and Harold's help, gets the courage to use T.E.R.D.S. to defeat the TP Mummy. He later appears to be crushing on Ms. Yewh at the end, much to Mr. Krupp's dismay.
In "The Shadowy Syndrome of Sinister Splotch", the titular villain takes control of his mind and body and uses his skills of invention to create bed of roses, a dryer sheet that allows him to control all robes, along with the wearer's of said robes. He then begins committing crimes while posing as Captain Underpants in order to frame and get rid of him. Luckily, George, Harold and Captain Underpants manage to defeat the villain near the end, saving him.
- He and Mr. Meaner and the only two Jerome Horwitz Elementary School staff members that have a sibling.