Duke Devlin

Ryuji Otogi, known in the English anime as Duke Devlin, invented the Dungeon Dice Monsters game. Otogi also owns a game shop called "Black Crown" that rivals the Kame Game Shop. (In the manga, the game shop is owned by Otogi's father, "Mr. Crown".) Duke challenges Yugi Mutou to a game of Dungeon Dice Monsters despite the fact that Yugi does not know how to play it. In the anime, Duke does this because Yugi defeated Maximillion Pegasus, the creator of Duel Monsters, smashing Duke's dreams of successfully making Dungeon Dice Monsters go world-wide. Duke believed Yugi cheated, and did not deserve to be the King of Games. Using Joey Wheeler, Duke was able to force Yugi to duel for Joey's freedom.

Yugi, however, manages to win, using some help from a laptop computer (which Duke included in all Dungeon Dice Monsters set-ups, supposedly to provide help to new players and give accurate statistics) Duke realizes that Yugi is not a cheater, and becomes friends with Yugi. Duke also received information from Pegasus's company that they decided to spread Dungeon Dice Monsters.

In the manga, Otogi is forced to have a Dungeon Dice Monsters duel with Yugi by his father, who was cursed by an ancient game he once played with Yugi's grandfather, Sugoroku. Otogi's father wanted revenge on Sugoroku by doing to his grandson what Sugoroku had done to him. He also wants his son Ryuji to become the new owner of the Millennium Puzzle. During the course of the game, Otogi's father smashes the Millennium Puzzle to pieces. Although Yugi succeeds in defeating Otogi, Otogi's father grabs Yugi and the Puzzle and takes it to a secret room where he attempts to piece the Puzzle back together again. However, doing this causes him to hallucinate about being trapped in a maze, and in his confusion he knocks over a candle, setting the building on fire. Yugi is forced to solve the Puzzle on his own in the burning building, and though he does, he faints, but is rescued by Jonouchi, (this situation is quite similar as to when Keith Howard dueled Yugi for the last time in the Battle City arc, after Keith smashed the Millennium Puzzle, he suffered hallucinations of Marik, and in his desire to get rid of the images, he grabs a length pipe and attacks but ends up shattering the arena power unit, causing a fire, Yugi was later saved by not only Joey, but Tristan as well).

Duke proves to be a quite important secondary character. Duke saves Serenity and Tristan from the Ghouls in Battle City, helps Joey when he collapses from his duel with Marik, and cheers for Yugi.

In the anime, he also helps Yugi, Jonouchi, and Seto Kaiba against the Doma Organization in the Waking the Dragons saga and also tags along during the KC Grand Prix and Ceremonial Battle sagas.

Deck
Duke plays a Dice Deck which is based around monsters from his own game, Dungeon Dice Monsters. It also includes Spell and Trap cards based on dice, making it a gamble deck.

