My MC is a teenage cadet at a military academy, where he has just been accepted to a prestigious officer training program. This program will blend book learning with in-field learning, and the commandant who leads it will be absolutely brutal. He'll be essentially the primary antagonist for the first part of this three-part story. I need him to be intimidating and imposing right from his introduction. I want the scene to be tense before he even enters the room, and then I want it to be clear that this class of young cadets is terrified of him. What are some ways that I can do this?