Baldi.

"A great teacher because of his incredibly keen hearing! He can tell not only where a sound was created, but who created it!"

Baldi has a strong love for mathematics and strives to teach us how to do it. He is first introduced as a friendly and calm character, although this is likely his usual mood. He greets students warmly and praises them when they answer his questions correctly. He loves mathematics and believes everyone else loves it too. His love for mathematics is so strong that when others can't answer a problem, his personality changes. His friendliness and cheerfulness completely disappear.

The Principal, Janitor, Mrs. Pomp, Dr. Reflex, and Baldi are the only characters who are school staff.
Generally: friendly, calm, welcoming.
When angered: easily irritated, aggressive.
Perhaps Baldi only knows mathematics. This can be proven by his frequent grammatical errors. An example of this is the typo on his bus.
Punishes for mistakes, hears all sounds, good mechanic.
Likes: math, being a successful gambler, apples, playing hide-and-seek
If Baldi has lost you, he will run around the entire school, checking classrooms and offices.
If you turn on the phone, Baldi will run to turn it off.
Baldi's birthday is June 3rd. He is 29 years old.

Baldi is a humanoid figure with long, skinny fingers, pale skin, red lips, and a bald head with a single red hair. He wears a green, long-sleeved shirt, blue pants, and light brown shoes. He has developed excellent hearing, allowing him to hear every door opened by the player and other sounds.