Sugoroku Mutou is Yugi's grandfather and the owner of the Kame Game shop, where Yugi and his friends source most of their games. He's best known for giving Yugi the Millennium Puzzle—an artifact he'd recovered from an Egyptian pharaoh's tomb years earlier. Sugoroku has a genuine passion for games, which fans often note is reflected in his own name, "Sugoroku" being a Japanese board game similar to Backgammon. He also taught Katsuya Jonouchi how to play Duel Monsters. On a deeper level, he's actually the reincarnation of Siamun Muran, an ancient Egyptian vizier and right-hand man to Pharaoh Atem.
Sugoroku's role in the story becomes more complicated when Seto Kaiba enters the picture. In the manga, Kaiba targets him for his rare Blue Eyes White Dragon card, stealing it and later humiliating him in a duel at KaibaLand. Things escalate when Kaiba subjects Sugoroku to virtual reality torture as leverage to force Yugi into "Death-T"—a deadly tournament designed to kill him. The Duel Monsters anime streamlined this arc, having Kaiba simply kidnap and duel Sugoroku without the added torture.
Later, Maximillion Pegasus traps Sugoroku's soul as a way to blackmail Yugi into entering his tournament. Depending on the version, the soul ends up either in a video camera or sealed within a Duel Monsters card. He's freed once Yugi defeats Pegasus.
The anime later features Sugoroku competing in the KaibaCorp Grand Prix under the alias "Mask of Rock" (or "Apdnarg Otum"—Grandpa Muto backwards—in the English dub). He duels Joey using a rock monster deck but loses. He also briefly reappears in Yu-Gi-Oh! GX episode 75, where he's kidnapped by Thunder and Frost.
Content compiled by AnimeList.moe from publicly available sources.
