Duke appeared in "Shine On, You Crazy Devlin". His voice is based on Snake from "The Simpsons", and almost every time he is speaking onscreen the music of "SexyBack" by Justin Timberlake plays in the background. Yugi says they can be friends if he gets rid of "that annoying theme music" to which Duke replied with "What theme music?" suggesting that he either can't hear the music or that the music has always followed him around so he thinks it's normal. He contradicts this in "Penguin Ex Machina", in which he says that he "can barely hear his theme music" and again in a deleted scene where Tristan finds a remote that changes it. In "Throw Haga From The Train", it's revealed that Duke must recharge his batteries on a daily basis; otherwise, his theme music will slow down and eventually stop entirely.
He often talks about how sexy he is and tries to convince people that Dungeon Dice Monsters is not like Duel Monsters, despite the similar rules and exact same monsters. When asked why it's different, he simply responds, "My game uses dice." In the end, everybody tells him that they consider his game more boring than Duel Monsters. However, Pegasus funds Dungeon Dice Monsters, apparently because it would make his card game look exciting by comparison.
Tristan thinks he's a witch, having seen him perform magic tricks, and can be heard constantly shouting "Burn the witch!", a reference to Monty Python and the Holy Grail.
When Duke reappears in "The Man Who Would Be Steve", he saves Tristan and Serenity from a mob of Steves. He throws a dice at one, prompting him to say that it "barely hurt". Tristan still refers to him as a witch at this point, asking him if he brought his broomstick with him while escaping the Steves. Men apparently propose to him all the time, (although Tristian claims that he was kidding). After reappearing Duke became part of Yugi's group of friends something he asked to be right before the start of season 2, even though he didn't fulfill his promise of losing the sexyback music.
Apparently his hand has a habit of touching other people's butts, as in "Final Deathstination". It has been mentioned that Duke is the fourth Jonas brother, likely a joke at his expense due to the many fangirls he has. Duke also seems to break the fourth wall (like everyone else) such as in "Chenquieh!" when he panics at the concept of dying and saying, "I can't believe I'm gonna' die in a show about f*cking card games!"
In "Beyond The Fourth Wall", he claims that waking up next to a blonde and a brunette (Joey & Tristan) is just another morning for him, as well as as replying a question from Tristan "Do you want aliens to probe your anus?!" with "maybe".
"Penguin Ex Machina" reveals that he has a disease where he dies if he doesn't have half naked girls applied to his body at regular intervals, this is notably shown by his theme music slowing down and losing its beat.
In "The Death Of Tristan Taylor", Duke partnered up with Tristan and Serenity in the Duel against Nezbitt. He was annoyed at Serenity's ineptitude in Dueling and Tristan's general stupidity, calling them "the worst three-way [he has] ever been part of". After Nezbitt transformed into Perfect Machine King, Duke challenged him to a theme music battle, playing the playdoughboy bootleg radio mix of SexyBack against Nezbitt's Super Giga Mecha Nezbitt theme. Duke lost when Nezbitt launched a barrage of missiles at him, "right up [his] sweet ass." However, he and Serenity won the entire Duel by showing Nezbitt a picture of Yuma Tsukumo, the (new at the time) protagonist of Yu-Gi-OH! ZEXAL. Yuma's illogical hairstyle overloaded Nezbitt's logic circuits, destroying him.
In "Stepbrother's Sin", Duke was the first of Yugi's friends to be turned to stone by Noah. He appeared in a fantasy, giving Yami a card. Later, in "It's a Mad, Mad, Mad, Mad Virtual World", he escaped the Virtual World with the others. Duke watched the rest of the Battle City tournament finals with the others. In "Winged Dragon of Rawr!", Duke left the group to host his own tournament, similar to the Battle City one: each contestant will have to ante their rarest dice.