Who is Teacher of the Day from Lost Names: Scenes from a Korean Boyhood and what is their importance?

Teacher of the Day inspected each class' rubber balls and let the class leave the field except for the boy's class. He counted 123 flat balls out of the sack when the teacher punched and slapped him. He asked why the teacher hit him when his class collected more balls than other classes. When asked why he ruined all the balls, the boy said they wouldn't all fit in one sack, and "it was rubber, really, that we were to collect, not the balls, as you surely understand, sir." The teacher dragged the boy to the principal's office and against the wall where he opens his pants to let them fall at his feet. The boy is hit several times with the bamboo until he refused to take any more. He ran his head into the teacher's belly and punched his groin to make him double up.