Sugoroku Mutou (Solomon Moto in the dub) is Yuugi's grandfather, and the owner of the Kame (Turtle) Game Store. It is not known whether he is Yuugi's maternal or paternal grandfather, but it's assumed that he is Yuugi's maternal grandfather, because for brief episodes in both the anime and the manga, Yuugi's mother was also shown living with Yuugi and Sugoroku above the Kame Game Store. (However, the fact that he shares the same last name as Yuugi may be indication that he is Yuugi's paternal grandfather. Series creator Kazuki Takahashi has said that Yuugi's father's absence in the manga is not indicative of a deceased parent, but that Yuugi's father is usually "away" on business. It is therefore likely that he too, lives with Yuugi, Sugoroku, and his wife when he is home in Domino.)
Prior to owning the store, Sugoroku Mutou traveled around the world, constantly seeking challenges and new games to play. He heard legend of the complex games in the Nameless Pharaoh's tomb, and traveled there to see if he could beat the games. The two Egyptians that led him there doublecrossed him, but both died as a result. Sugoroku nearly died himself, but he managed to solve all the puzzles and reach the final stretch in the tomb's labyrinth before falling unconscious. He only remembered seeing the silhouette of someone reaching down to him, calling him "Siamun"...
Since he was technically "defeated" in the tombs, Sugoroku kept to his promise that he would trade his tuxedo for a pair of overalls and never leave his home again. However, he still duels and is considered an expert on games. In interviews, Kazuki Takahashi has said that Sugoroku's store doesn't stock video games or the like, only traditional games, ethnic games, and of course, Magic and Wizards (Duel Monsters) cards.
Sugoroku was the original owner of the fourth Blue-Eyes White Dragon card, which Seto Kaiba aimed to own. In the manga, Kaiba dueled Sugoroku for the Blue-Eyes, and nearly gave Sugoroku a heart attack by using the three other Blue-Eyes in a virtual attack against him. Not long after, Kaiba ripped up the fourth Blue-Eyes card. Similar events happened in the manga.
In the anime, Sugoroku was said to have received the card from his friend, Arthur Hopkins (Hawkins in the dub) after beating him in a game. Hopkins' granddaughter, [[Rebecca Hopkins] didn't know of this game, and accused Yuugi of stealing the card, so she challenged him to a duel to get the (ripped up) card back.
Sugoroku is the reincarnation of Siamun Muran, the former holder of the Millennium Key and the advisor of the Pharaoh. He is called Shimon in the video games, but his face is almost always concelealed up to his eyes. In the Duelists of the Roses game for the Playstation 2, he was called Jasper Dice Tudor, and in early Playstation games, a Sugoroku-like helper was often called Paradox (not to be confused with the Labyrinth Player Killer duelists in Pegasus' Duelist Kingdom arc).
In the KC Grand Prix Yu-Gi-Oh Duel Monsters filler arc, Sugoroku Mutou disgused himself as a top-notch duelist known as "Mask the Rokku," (Roku means "six" in Japanese, and "Sugoroku" means "double six." Sugoroku is also the name of a Backgammon-like game in Japan. "Rokku" actually is the Japanese pronunciation of the English word "Rock," but because he wore a "six" on his mask, the word was clearly intended to be a pun). In the English dub, Solomon's alias was Otom Apdnarg, which, spelled backward is "Grandpa Moto." He uses a variety of older Duel Monsters cards to surprise Katsuya Jounouchi, whom he duels against. Though Yuugi and the others catch on to Sugoroku's trick very quickly, Jounouchi doesn't realize that the duelist he faces and Yuugi's grandfather are one and the same until the end of the duel.
Birthday: October 4th, 1917 (Libra) - 72 years old by Battle City
Height: 151 cm (approximately 4'9")
Weight: 62 kg (approximately 136.68 pounds)
Blood Type: O
Favorite Food: Japanese rolled egg omelet
Least Favorite Food: Nothing in particular
Voice Actors: Takeshi Aono (Toei's Yu-Gi-Oh!), Tadashi Miyazawa (Yu-Gi-Oh! Duel Monsters), Adam Blaustein (English dub)