| Dewey Finn | |
 | |
| Nickname | Mr. S |
| Age | 30 |
| Occupation | Rocker Fake substitute teacher (formally) Music Teacher. |
| Band Job | Guitarist/Lead Singer |
| Portrayer | Jack Black |
Dewey Finn is a down-on-his-luck, energetic, 30-year old, wannabe rock superstar who at the very start of the film is kicked out of his own band No Vacancy due to his antics such as constant 20 minute solos and stage diving.
Dewey is unemployed but is forced to try and find a job after Ned and his girlfriend,Patty, threaten to kick him out of their apartment due to Dewey not paying his share of the rent. In the film Dewey gets a job as a substitute teacher for Horace Green Prep School by pretending to be his friend Ned Schneebly. Dewey starts the movie as a self-centered, egotistical, energetic rocker who was not very intelligent in areas other than rock. By the end of the movie he becomes much kinder, more likable, and becomes a great music teacher.
When walking past the class' music class in his spare time, he discovers the students are musically talented and decides to make them into a rock band and compete in the battle of the bands and get revenge on his old band. He manages to get the class to go along with the idea by telling them that it is a school project and if they keep it secret from the other staff, they can start before the others. Dewey and the class manage to keep their band practices secret from the rest of the school by blacking out windows, sound-proofing the classroom and placing cameras to watch the hallways. He is eventually exposed at Parent's night at the school but runs away with the kids and plays at the Battle of the Bands. Later, he forms his own after school program for the kids. Thanks to battle of bands they have a lot of potential gigs and record offers that Summer made the deals on her cell phone.