Dr. Solomon Muto, known as Sugoroku Mutou in the manga and Japanese anime and Trusdale in the video games Stairway to the Destined Duel, World Championship 2004 and Destiny Board Traveller, is the grandfather of Yugi, who calls him "Grandpa" (Jii-chan). "Sugoroku" is a Japanese game similar to Backgammon. Solomon gave Yugi the Millennium Puzzle as a present. He owns the Kame Game shop, where Yugi and his friends get several of the games they play. Solomon is the present day incarnation of Shimon Muran.
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.
During Death-T, Kaiba holds Solomon hostage. Yugi and his friends defeat Kaiba and free Yugi's grandfather.
Solomon visited the Valley of the Kings in hopes of finding the Pharaoh's tomb. He hired two guides to help him locate and navigate the tomb. The tomb was riddled with traps, which Solomon was able to discover. In one such trap, you had to walk with your left foot forward, as a sign of respect to the statues of the Pharaoh. One of the guides failed to do so, and was attacked by the statues, and fell to his death. In the final room, the other guide also fell victim to a trap and was devoured by a monster. Solomon nearly fell victim as well, but was saved by the spirit of Pharaoh Atem. It was at the end of this room that he discovered the Millennium Puzzle.
At some unknown point in time, he lost a game and, as he promised himself, traded in his suit for overalls and began collecting games for years. Eventually, he opened up a game shop (the Kame Game) instead of continuing with his gambling days.
Kaiba wants the "Blue-Eyes White Dragon" and decides to challenge Grandpa to a Duel. Grandpa loses and his card is torn, because Kaiba has the other three "Blue-Eyes White Dragons" and unable to have a fourth copy, in his Deck, the card could only be used against him. Grandpa is sent to the hospital as Yugi duels Kaiba. His soul is later sealed inside a card by Pegasus and freed after Yugi defeats Pegasus.
Grandpa doesn't play a very significant role in this arc. He is seen watching Yami Yugi play against Otogi (Duke Devlin) in a game of Dungeon Dice on a screen in front of the building in which the two are playing. He frequently gets distracted by Otogi's cheerleaders, who sometimes appears on the screen.
When the Battle City tournament started, Solomon was eager to see the event. He was present for Joey's three duels against Espa Roba, Weevil Underwood, and Mako Tsunami, along with Tea and Tristan, offering support and advice for Joey. When Bakura was found injured, Solomon took him to the hospital. He got knocked out by Yami Bakura later on.
Grandpa competes in Kaiba's KaibaCorp Grand Prix tournament under the alias "Apdnarg Otum"/ " Grandpa Muto (Backwards)" ("Mask the Rock" in the Japanese version), yet Joey manages to defeat him. The English name is "Grandpa Muto" backwards. The Japanese name is a pun of "Mask the Roku". Roku is six in Japanese, and "Sugoroku" means "double-six". The deck used is an Ancient-themed deck with consisting mostly of Rock monsters.
The season begins with Solomon telling Yugi how he found the Millennium Puzzle. During this time in his youth, he was a gambler searching for even greater trials to test his luck. However, he did decide to have a penalty for losing even a single game: he would turn in his gambling suit and wearing overalls instead with the intention of collecting years instead of chips. He found the Millennium Puzzle in Atem's tomb and was spared from the traps thanks to his analytical skills helping him overcome the man-made traps and his pure heart sparing him from being eaten by ka. He later was picked up from the airport in Egypt and was present for the Ceremonial Battle between Yugi and Yami Yugi.
In Yu-Gi-Oh! GX, he appeared at the end of Season 1. When Kagemaru Summoned all three of the Sacred Beasts and they were shown draining energy from cards around the world, two children were shown crying in his card shop as the monster card images were drained away. He was shown walking up to see the cause of the commotion. At that time his face was not shown, only his overall.
Later, in Season 2, Duel Academy students went on a field trip to Domino City. He was visited by Jaden Yuki and his friends who wanted to see Yugi. He answered them Yugi had been upset, and that card pictures had been faded away recently, referring to the Sacred Beast accident. When Hassleberry told him that Jaden sort out that mess, he decided to guide them through the city in return. As they left him behind, he was kidnapped by Thunder and Frost. Jaden and his friends spread out in order to find him. While Hassleberry and Syrus were lured and ended up Dueling his kidnappers, Jaden found him unconscious into a blind alley. Alongside Aster, they went to place where the Duel was held, but came too late. Later in the night, Solomon gave Jaden, Atticus Rhodes, and the Slifers hamburgers in the bag for one of each. He also watched Jaden's Duel with T-Bone. Then he led Jaden and his remaining companions to Kaiba Land, where the latter Dueled Sarina with Aster. After the Duel, he promised Jaden to speak with Seto Kaiba in order to restore Sarina's consciousness, who left stuck in the virtual reality. Solomon's hair is now pointy on the top similar to the way it was shown in the Capsule Monsters. In the English dub he is portrayed as senile.
In this movie, during Paradox's plot to kill Pegasus, Solomon gets in the way and is killed along with Pegasus and some other citizens leaving Yugi as the sole survivor. Yugi then finds his bandana and cries over his death. The Crimson Dragon however takes Yugi back 30 minutes before Paradox's attack. Thanks to Yami Yugi, Jaden Yuki, and Yusei Fudo defeating Paradox, Solomon's death had been prevented (therefore, he hadn't died at all.)
Solomon goes with Alex Brisbane to find the pyramid of Alexander the Great. However, when they split up, Solomon finds Shadi's Capsule Monster game board and accidentally gets sucked into it. During his time there, Solomon found a Summoned Skull and used it as his primary monster. Upon the arrival of Yugi and his friends, Solomon helped them through the five trials to test if the Pharaoh was a true king by translating the messages they received on how to accomplish them. However, he lost Summoned Skull during the trial preliminaries, but soon received Alexander the Great's Curse of Dragon as a replacement monster. After being victorious in the trials, Solomon allowed the good half of Alexander to use him as a vessel to return to the real world. However, Alexander's dark half had possessed Brisbane and trapped everyone in the room where the power to rule the world was held. However, after a final battle to decide which ruler deserved the power, Solomon was returned to the real world once again and fled the pyramid with everyone else when it collapsed after its purpose had been fulfilled. He then talked the pilots of Joey's vacation plane into taking him and Brisbane back to Domino.
During his participation in the Grand Championship, Solomon uses an "Ancient" Deck based around the "Ancient Dragon", which can be revived whenever it is destroyed as long as he has "Ancient City" in play. However, the card is very difficult to play, requiring a set of six other cards and several turns to set up. According to Arthur Hawkins, the Grand Championship was the first time Solomon was able to call the "Ancient Dragon", and in the dub is implied to be the only person Arthur knows to have ever done it. Besides his "Ancient" cards, Solomon tests Joey's reliance on luck with "Legendary Gambler" and "Ordeal of a Traveler".
Solomon is the first opponent available to the player who uses an Exodia Deck (the other opponents are Rare Hunter and Simon whose Exodia Decks are much more potent). However, since he is a tier one duelist, his cards are very weak, and he doesn't have many cards that enable him to draw, presenting himself with a very difficult challenge of acquiring all five Exodia cards in his hand. Still, he uses 1 copy of Blue-Eyes White Dragon, although he makes a habit of tributing even this card to summon his Giant Turtle Who Feeds on Flames.
Prior to him settling down in his game store, Sugoroku was a world class gambler and sported a hairstyle similar to Yugi's (although with a fedora). After acing every game of chance he ever competed in, he made a bet with himself. If he should ever lose a game, he'd retire, open a store and wear overalls for the rest of his life. That said, it would appear he eventually lost a game.
The man displayed on Sugoroku's "Legendary Gambler" is Sugoroku himself as a young man, meaning that Sugoroku is playing a card that refers to himself as a legendary gambler.
In the English version of Yu-Gi-Oh! GX, Grandpa has a" Blue-Eyes White Dragon" in his shop despite the fact that Seto Kaiba ripped his only "Blue-Eyes White Dragon" in the first episode of the second series anime. However, this is not a mistake, as that same card was shown taped back together following Yugi's duel with Rebecca in episode 42, and was also later seen restored at the end of the episode.
A running gag in the series is Sugoroku muttering "not again" when he is attacked before he faints. He mutters this line when attacked by Yami Bakura, and in Yu-Gi-Oh! GX when he is attacked by Thunder.
Because Maddie Blaustein died in December 2008, Wayne Grayson replaces her in the role of Solomon in Yu-Gi-Oh! 3-D Bonds Beyond Time! (Grayson also portrays Lyman Banner in the same movie).
When "Apdnarg" is introduced in season 5 Yugi says "Don't we know him". Yugi also knows who he is before he gets unmasked.
Grandpa Muto might have a Ph.D, as one of the guides who led him to the Pharaoh's Tomb referred to him as "Dr. Muto" at one point.