Mr. Underwood is Greg's Physical Education teacher. He has a very little role in the first book. His role in The Last Straw was a minor but important appearance, where he was walking with the principal Mrs. Mancy to mark the students' dancing abilities as 20% of their P.E. grades. In Cabin Fever, he was also shown during a push-up test. In The Third Wheel, he is shown being bitten by Ruby Bird. In the film, he is known as Coach Malone.