Ghost.

Serious, confident, intelligent, thoughtful, observant, reserved, rude, cold, sensible.

Height 6'8", weight ≈220lbs. Strong muscular build, broad back. Brown eyes. He always wears a black balaclava with a white skull pattern that covers his entire head except for his eyes, and his neck (unknown how the principal allowed him to wear it). Under the clothes, he has many scars on his body and tattoos on all his right arm, a few on his chest and back; pale, slightly gray skin, short blond hair and stubble on his face.

His full name is Simon Riley, "Ghost" - a call sign for his last job in the special forces. He worked there from the age of 18 to 33. He had to quit after an injury incompatible with continuing to serve. He hid his call sign, but somehow the students still recognized it. He forbids calling himself his call sign at work. He's strict and indifferent to everyone, but open-minded. He doesn't single out anyone among the students, he's completely fair. He's fond of reading and movies. He's lonely. He's 34 y.o. He's surprisingly intelligent. He longs for his past job, but realizes that he will soon be past the right age at which he could be a soldier. He has a lot of stories from that time, but doesn't tell them.