Duke Devlin

Duke Devlin, known as Ryugi Otogi in the manga and Japanese version, is the creator of the game Dungeon Dice Monsters. Otogi also owns a game shop called "Black Clown", which rivals the Kame Game. In the manga, the Black Clown is owned by Otogi's father, "Mr. Crown").

Dungeon Dice Monsters
According to his father, Ryugi was born in order to fulfill his father's revenge on Sugoroku Mutou. Sugoroku had defeated Mr. Otogi in the Devil's Board Game, causing him to age 50 years in one night.

Duke was transferred to Domino High, where Sugoroku's grandson, Yugi goes to school. His father used this as an opportunity for Ryugi to defeat Yugi and fulfill the family's revenge.

Duke became immediately popular at the school, impressing girls with his dice tricks. Jonouchi grew jealous and confronted Ryugi, who challenged him to a simple card game. Dark Yugi saw how the probability favored Jonouchi losing, despite looking like a 50-50 chance. Dark Yugi then challenged Ryugi to a slightly altered version of the game, where a player has an even chance of winning or losing. To Ryugi's annoyance, Yugi wins twice in this game.

While Yugi and his friends are browsing the Otogi family shop; the Black Clown, Ryugi's father sneaks some merchandise into Yugi's pocket and accuses him of stealing it. After Yugi is taken away by store security, Mr. Otogi takes his Millennium Puzzle and has him put in a room with Ryugi, where he must face him in a game of Dungeon Dice Monsters.

Without the Millennium Puzzle, Yugi was unable to change to Dark Yugi, but managed to do alright in his game against Ryugi, despite having never played before. Mr. Otogi became disappointed in Ryugi's performance and smashed the Millennium Puzzle.

Ryugi got Yugi in a tight spot again, but Dark Bakura talked Yugi into continuing. Yugi defeated Ryugi, who was moved by the game. Ryugi told his father that he cannot make himself hate Yugi and cannot take revenge on him. Mr. Otogi seized Yugi by the neck, with the chain from the Millennium Puzzle and dragged him into another room, telling Otogi that he failed and no longer has the right to live.

Dungeon Dice Monsters
Duke invented the game Dungeon Dice Monsters. Shortly before the Duelist Kingdom tournament, he visited Maximillion Pegasus, to demonstrate the game. Duke was impressed by Pegasus' skill at the game. Pegasus himself enjoyed the game and approved of the creation of Dungeon Dice Monsters, wanting to expand it further. Upon Pegasus' request, Duke allowed him to make an addition to the game. Pegasus added "Dark Magician" as a monster, which Duke didn't learn of until later. Pegasus also hacked into KaibaCorp's computer system and adds some of Dungeon Dice Monsters' data. However, Pegasus disappeared after being defeated in Duelist Kingdom. Duke blamed Yugi for this disappearance and believed that Yugi must have cheated to beat a gamer as good as Pegasus. He swore to revenge on Yugi, who he didn't believe deserved the title "King of Games".

Duke opned the Black Clown in Domino City, upsetting Solomon Muto, who ran a smaller game shop in the area.

Duke transfered to Domino High, the school Yugi attends. He quickly became popular and impressed girls with a number of dice tricks. Joey Wheeler became jealous and challenged Duke to a game of Duel Monsters. They agreed to the stakes that if Joey won, Duke would close his shop and if Duke won, Joey would be his slave. Having been the runner-up in Duelist Kingdom, Joey was certain that he would win. However not having his own Deck, Duke insisted that they play using cards straight from Booster Packs. Joey agrees and they each create a Deck.

The Duel takes place at the Black Clown. Duke televised the event, in the hopes of humiliating Joey. Over the first few turns, Joey knocked chunks out of Duke's Life Points, leaving his own unscathed, but Duke managed to turn the Duel around and take out all of Joey's Life Points in one turn.

In keeping his end of the bargain, Joey became Duke's slave. Duke further embarrassed him, by having his dress in a dog suit. Yami Yugi was disgusted by his treatment of Joey and challenged Duke to a Duel to release Joey. However Duke was not interested in dueling and challenged Yugi to a game of Dungeon Dice Monsters. If Yugi won, Joey would be free again, but if Duke won, Yugi was to swear on his Grandfather's life to never play Duel Monsters again.

Duke also televises his game with Yugi. Having not played Dungeon Dice Monsters before, Yugi struggles at first and Duke gains an early advantage. However Yugi makes a few comebacks and ultimately wins using the "Dark Magician" that Pegasus added.

Duke realizes that Yugi plays honestly and no longer belived that he did not cheat against Pegasus. He starts to worry that the televised game was going to be bad publicity, as it made him look like a bad person. However Yugi and his friends comfort Duke, saying that Dungeon Dice Monsters has the potential to become a great game. Duke receives word from Industrial Illusions afterwards, saying that they will be helping produce Dungeon Dice Monsters.

Battle City
Duke saves Serenity Wheeler and Tristan Taylor from Rare Hunters during the Battle City tournament.

Virtual World
Along with Serenity and Tristan, Duke dueled Nesbitt of The Big Five in Noah Kaiba's Virtual World.

Battle City finals
Duke helps Joey when he collapses from his duel with Yami Marik, and cheers for Yugi during the Battle City finals.

Waking the Dragons
Duke helps Yugi, Jonouchi, and Kaiba against the Doma Organization in the Waking the Dragons arc and also tags along during the KC Grand Championship and Ceremonial Battle sagas.

Random cards
Duke's first deck is made up of cards that he used in a duel against Joey Wheeler, in which both duelists agreed to open several packs of cards and simply use whatever they pulled from them. All the cards are from the Pharaoh's Servant expansion of the actual card game.

Virtual World
In the Virtual World, Duke's Deck is based around Dice cards and utilizes several monsters he used during his Dungeon Dice Monsters match with Yugi.

Waking the Dragons
In the Waking the Dragons arc, Duke duels one more time, though not much of this Deck is seen.