Lou Zarr is a stiff and humorless man who occasionally teaches Trigular Calcometry at Monster High. He demands respect from his students, but both his uncompromising attitude and name, which sounds like "loser", only bring about mockery. His methods of education aren't much better: Lou Zarr's lessons are so boring that his way of teaching even puts himself to sleep.
It may be he is not very fond of monsters or teenagers, as he has referred to his students as "little freaks".
Lou Zarr takes over Trigular Calcometry 101 from Headless Headmistress Bloodgood. His demeaning attitude towards the students and intent to do the whole book don't earn him any friends. When Deuce Gorgon enters the classroom late, Lou Zarr insists that he take off his sunglasses. Deuce complies and thus petrifies Zarr. While the other students dismiss themselves, Deuce stays behind a little longer to inform Mr. Zarr that the effect wears off after a few hours... usually.
Lou Zarr hosts Trigular Calcometry 101, Frankie Stein's very first class. It makes her worry she won't survive school. In fact, Zarr's lesson is so boring he makes himself fall asleep mid-calculation. When a little later the school bell rings, the students leave swiftly, except for Ghoulia Yelps. She stays to finish Mr. Zarr's calculations; Zarr only waking up in confusion after she has completed the task.