Mr. E. was a substitute teacher filling in for Miss Grotke in the episode "The Substitute". This was because she was sick for a week. Although it is a rather obvious play on the word "mystery", his full name is never revealed. He has zero fear, he is strict and his teaching style is somewhat harsh. He later is revealed to have a soft side, because T.J.'s project "touched him." Apparently, he has had experience teaching in Southeast Asia, Yugoslavia, and The Bronx (New York City) prior to his time at Third Street. Mr. E.'s teaching style is a radical change of pace for the class; however, the class comes to appreciate him in their own way.
A strict disciplinarian, he demands obedience and dislikes when people talk back to him. His punishments can be somewhat severe, but deep down he is actually a good person. He is able to see the best aspects of his students and bring them out through his radical teaching, which differs from the standard curriculum. It is also shown that he does care for his students, as he helps Gus stand up to a bully and kindly gives them advice to help each of them with their project, earning each of his students' (including at the very end even T.J.'s) respect. He respects loyalty, evident when he applauds T.J. for his project which is a get well card for his teacher Miss Grotke. Considering the implications he was involved with the US military, it explains his strict personality.
He is a tall, handsome man who wears a business type suit consisting of a black suit with a green vest underneath and a white button shirt with a black tie. The Ashleys at one point refer to him as dreamy, implying he is considered attractive especially since they are very particular about fashion and looks.
- He also makes a cameo appearance in the first part of "Lawson and His Crew;" applauding after Randall and Kurst's dance recital. This is a reference to Mikey and Spinelli's recital in the episode "Dance Lessons."
- The name, Mr. E., is a play on the word "mystery," a typical ploy in English literature.