Principal Brenigan is the principal of Mesa High School, in his office are cameras that watched students in hallways.
He:
Caught Mo and Scott wandering in the hall skipping class
Caught Olivia hiding in the janitor's closet reading a novel
Put Stella in detention for interrupting him in an assembly
He seems to hate Lemonade Mouth and is a fan of Mudslide Crush. He moves clubs and groups that he doesn't like into the basement. Instead, he takes charge of varsity teams and cheerleading squads up on the school and has a giant gym instead of a music room. He is sponsered by a sports drink and would do anything to stop Lemonade Mouth (As in when the Halloween Bash was over, the next day, they were in the office and he threatened to suspend them if he even hear a hum out of them) He rides on a Segway PT for a transportation in hallways.
At the end of the movie, He starts to like Mel's Lemonade and the new music hall