Our math teacher is known as a real tartar, and all the students are afraid of him.

tartar 原指"鞑靼人"，历史上鞑靼人以勇猛善战著称。在英语中引申为"严厉可怕的人"，常用来形容要求严格、令人生畏的老师或上司。这个词带有比喻色彩，强调其令人畏惧的特质。