Teacher (or most known as The Narrator) is a main character of the Shut Up! Cartoons series, Do's & Don'ts.
Though he's only a voice and appears in every episode, he is considered to be one of the main characters. The Narrator (Teacher) teaches the kids about what the episode focuses on, and what they should/shouldn't do. (Hence the name of the cartoon). Before the Season 2 Premiere episode, he was referred to by fans as "The Narrator" though in the episode, Jimmy and Clyde refer to him as "Teacher"