Mr. Rotter is a phantom and presumably from Romania, who teaches Dead Languages at Monster High. He was introduced in the webisode "Idol Threat". In his first appearance, he was voiced by Yuri Lowenthal. Currently, he is voiced by Cam Clarke.
Mr. Rotter believes in order and has little patience for students that try to cause chaos. He is, however, not a strict teacher and enjoys to spark enthusiasm for both his classes and the other ones in the students. This means that sometimes Rotter fails to understand when students are not enthusiastic about some of the classes. He is known for never giving 'A's.
Rotter has grey-to-green skin and sandy hair. He is usually dressed in a brown coat.