Dr. Mertz is a science teacher. Despite having a tough curriculum, he tries to make his class enjoyable to students. One of his means is to give a trinket molecule hat to Screech; his star pupil. When Kelly is in danger of failing his class and thus face being grounded by her parents, Screech offers to tutor her. Screech's tutelage seems to work as Kelly does well on the midterm.
He was only featured in one episode.