Mr. Stein, known in Japan as Professor Kouji Satou 「佐藤浩二, Satō Kōji」, is a Duel Academy professor only seen in the third season, though flashbacks indicate he was present in the first year, seeing as Chumley appears in one of them. A former Pro League Duelist who came from a poverty-stricken family, Mr. Stein fosters a grudge towards Jaden Yuki for ruining the interest of other students in his lectures because of the boy's position as the academy's top Duelist despite having his horrendous grades. This sets an example for others that they don't need to study to succeed, causing most of them opting to sleep through his classes. His grudge increased when his one good student, Alexis Rhodes, ditched his class, sending him over the edge.