He was portrayed by Don Creech.
He is shown to dislike Ned and Cookie, mostly because of their crazy schemes. He is often shown as the show's antagonist. Sometimes, he is just teaching Ned, Cookie, and Moze a lesson. Sweeney also wants his students to succeed. He has a dislike for cell phones as shown in the episode "Cell Phones". He is always shown with a lab coat except for the Episode "School Car Wash".
Sweeney is what Ned considers to be "an evil teacher who's out to destroy you". He is an evil scientist and teacher at James K. Polk Middle School. As the series progresses, he shows more of his kind side and develops respect for his students.
In the series finale, Mr. Sweeney helps Ned hide from Vice Principal Crubbs as an early graduation present. He later tells Ned that "I'll always remember you as one of my worst students, but also one of my favorites."