Duke Devlin

Duke Devlin, known as Ryuji Otogi in the manga and Japanese version, is the creator of the game Dungeon Dice Monsters. Duke also owns the "Black Clown" game shop, which rivals the Kame Game. In the manga, the Black Clown is owned by his father, "Mr. Clown".

Anime intro
In the anime, Duke invented the game Dungeon Dice Monsters and visited Maximillion Pegasus to demonstrate the game shortly before the Duelist Kingdom tournament. 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 additions to the game, like the "Dark Magician" as a monster and also hacked into KaibaCorp's computer system to adds some of the data of Dungeon Dice Monsters. However, Pegasus disappeared after being defeated by Yugi Muto in the Duelist Kingdom tournament, 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".

After the Duelist Kingdom tournament, Duke opened the Black Clown (a rival game shop to the Kame Game) and was transferred to Domino High School, the school that 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 him 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 determined that he wouldn't have cheated 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 afterward, saying that they will be helping produce Dungeon Dice Monsters.

Manga intro
According to his father, Ryuji was born in order to fulfill his father's revenge on Solomon Muto. 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 School, where Yugi Muto (Sugoroku's grandson) goes to school. His father used this as an opportunity for Ryuji 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 Ryuji, who challenged him to a simple card game. Yami Yugi saw how the probability favored Jonouchi losing, despite looking like a 50-50 chance. Dark Yugi then challenged Ryuji to a slightly altered version of the game, where a player has an even chance of winning or losing. To Ryuji's annoyance, Yugi wins twice in this game.

While Yugi and his friends are browsing the Otogi family shop; the Black Clown, Ryuji'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 Ryuji, 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 Ryuji, despite having never played before. Mr. Otogi became disappointed in Ryuji's performance and smashed the Millennium Puzzle.

Ryuji got Yugi in a tight spot again, but Yami Bakura talked Yugi into continuing. Yugi defeated Ryuji, who was moved by the game. Ryuji 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. After his father's secret room became engulfed in fire, Otogi took his father out of the way while Yugi recompleted the Millenium Puzzle and then was rescued by Jonouchi.

Battle City
Duke saves Serenity Wheeler and Tristan Taylor from Rare Hunters during Seto Kaiba's Battle City tournament, meeting Mai Valentine in the process. He watches the rest of the tournament along with the other characters. He is shown having a crush on Serenity, much to Tristan's disgust.

Virtual World
Along with Serenity and Tristan, Duke dueled Nesbitt of The Big Five in Noah Kaiba's Virtual World. He confidently told Nesbitt, "You may not know me, but dice are my specialty".

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, Joey, 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. During the Dawn of the Duel saga, he helped take care of Yugi's grandpa, and contacted Yugi's friends & other important people such as Maximillion Pegasus about Yugi's absence (offscreen).

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, made mostly of Zombies.

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