Sugoroku Mutou is a character in the Toei Yu-Gi-Oh! anime. He is the grandfather of Yugi Mutou. This is the series incarnation of Sugoroku Mutou, from the manga.
Seeing Yugi still working on the Millennium Puzzle after eight years, Sugoroku said that the puzzle was beyond normal human understanding and reminded him that the archaeologists who discovered the puzzle all died mysterious deaths. However, Yugi wasn't worried and ran away from his grandfather, who tried to take the puzzle so he could sell it.
Another day, Sugoroku noticed that Yugi was going to leave for a while. Sugoroku told him that his chores were not done, but Yugi replied that he would hang out with his friends. His grandfather was glad that Yugi was joining his friends, since he rarely did so.
During Death-T, Kaiba holds Sugoroku hostage. Yugi and his friends defeat Kaiba and free him.