In the 2003 film School of Rock, Jack Black’s character uses the name “Mr. S” while posing as a teacher.
Black plays Dewey Finn, a struggling guitarist who impersonates his roommate, Ned Schneebly, to obtain substitute-teaching work at the Horace Green prep school. When Dewey arrives, he does not actually know how to spell Schneebly and adopts the shortened classroom name “Mr. S.”
Dewey soon abandons the planned curriculum and forms a rock band from the fifth-grade students. He assigns the children musical roles and prepares them for the Battle of the Bands.
The character’s false teacher identity drives the film’s central comedy. Mr. S is not Dewey’s real name, and Ned Schneebly is the person whose identity he initially steals.