Bandit Keith, whose real name is Keith Howard, is the former U.S. Duel Monsters Champion. In the original Japanese manga, he was first referenced by Seto Kaiba as a Card Professor, one of many famous Duelists who were known for winning the prizes in large Dueling tournaments. He was so successful in this profession, that his reputation earned him the nickname "Bandit Keith".
In the English manga, many of his dialogues have been modified to contain many censored profanity, to indicate his lack of respect for others.
During the final round of the Intercontinental Championship tournament in New York City, Keith was up against Maximillion Pegasus, who used his Millennium Eye to read Keith's mind and predict his moves. Afterwards he wrote something down on a piece of paper and calls over a kid named Sam from the audience. He tells the kid to Duel against Keith using the instructions on his note. Using it, the kid defeats Keith in one turn. Keith, shocked and humiliated at being defeated by a child, fell into depression. In the manga, he even tried to drown his pain with drugs and alcohol, and eventually ended up in the underground gambling circuit, playing Russian Roulette for money, as he had nothing more to lose. He later sneaks into Duelist Kingdom to defeat Pegasus and reclaim his glory.
In Duelist Kingdom, he trains three Duelists; Zygor, Sid and a Ghost and Zombie Duelist named Bonz (secretly intending to use them for their starchips). He has Bonz Duel Joey Wheeler and lends Bonz several rare cards, including the powerful "Call of the Haunted", to strengthen his Deck. Although Keith directs nearly all of Bonz's moves, he still loses. Afterward, Keith calls Bonz a loser and ignores Joey's challenge for a Duel face-to-face. After leaving the arena, Keith traps the heroes in the cave, then attacks his own minions and steals their star chips, giving him enough to enter the castle as the first finalist. Later, he is surprised to see Yugi on top of the tower (not knowing that Yugi and his friends had managed to escape from the cave after defeating the Paradox Brothers), and is also quite surprised to see Kaiba as well.
Keith later Duels Joey in the semi-finals of Duelist Kingdom. He unveils a rather devastating Deck of Machine cards. His Machine cards not only have superior firepower over Joey, but also are immune to any sort of magical attacks (this is not a real rule). Keith cheats by pulling cards out from underneath his wristband to power up his monsters, but Joey still wins. Afterwards, Keith claims that Joey should be disqualified since the card he used to enter the semi-finals wasn't his. Joey admits that Mai gave him her card, but then asks how Keith knew that his card didn't belong to him. Pegasus chuckles and explains that Keith obviously stole the card, citing evidence of how he came to the conclusion (earlier, Keith was sure Joey would not be able to find his entry card because Keith had it himself). Joey and the gang then say that Keith should be disqualified, and Pegasus agrees, but not just because of his thievery. He tells Joey that Keith was keeping his "7 Completed" cards beneath his wristband, allowing him to use them when needed, and orders his security guards to take Keith away. So, Pegasus disqualifies Bandit Keith personally for cheating and stealing. Keith breaks away and confronts Pegasus. He points a gun at his head (but the gun is removed in the dubbed anime) and demands the 3 million dollars prize money for the tournament. Pegasus is calm and just makes fun of Keith, telling him that he had sunk to being the worst criminal scum ever since the former defeated him. Keith steps forward, and Pegasus moves his foot to hit a hidden button. The floor around him falls away, and Keith plummets down a tunnel into the ocean.
In the manga, Pegasus did not order his guards to take away Keith after the match was over, as Keith left the arena right after and headed off to intercept Pegasus in the hallway; he threatens Pegasus with a knife for the prize money. Pegasus uses his Millennium Item to cast a Penalty Game on Keith, "turning" Keith's hand into a gun. This makes Keith finally understand that Pegasus indeed has magic, rather than cheating through their previous Duel in the first tournament as he had previously thought. The hand "shoots" Keith, “killing” him instantly.
Battle City (anime only)
In the anime, while struggling against the ocean currents, he was rescued by Rare Hunters, and became under the control of Marik Ishtar. Disguised as a fortune teller, Keith asks Yugi Muto if he can see his Millennium Puzzle. When Yugi hands it over, Keith steals the Puzzle and flees to a hidden arena. Chaining the Puzzle to the arena, Keith says the only way for Yugi to reclaim the Puzzle is to Duel for it. (In the English anime, Marik has Keith Duel Yugi to win the Puzzle for him. In the Japanese anime, Marik has Keith Duel Yugi in the hopes Dark Yugi will appear.)
Although Keith is hooded, Yugi quickly deduces his identity from his Machine Deck. At this point, Marik reveals that he and his Rare Hunters rescued Keith after he was dumped into the ocean by Pegasus. He then took him under his control. Keith's Deck, augmented with rare cards courtesy of the Rare Hunters as well as him hiding cards under his robe's sleeves much as he cheated in Duelist Kingdom, surprisingly begins to defeat Yugi. However, the Duel is watched by Yami Bakura. He senses the dark energies from Keith, and realizes he has been hypnotized. He refuses to let Yugi lose and forfeit the Puzzle, since he wants it for himself, and uses the Millennium Ring to break Marik's control of Keith. While Marik and Keith struggle for control, Keith shatters the Puzzle against the console (In the English anime, he does this because Marik commands him to. In the Japanese anime, Keith does it himself because he thinks the voice trying to control him is the spirit of the Puzzle). Yami Bakura then swings down, knocking Keith off the arena.
While Yami Bakura leaves Yugi to put the Puzzle back together, Keith hallucinates that Marik is nearby, giving him orders. Grabbing a length of pipe and attacking the images, Keith shatters the arena power unit, causing a fire. While the building burns, Joey and Tristan break down the door. A terrified Keith runs past them, claiming the arena is haunted.
Waking the Dragons
Keith's "lost soul" is seen when Yami Yugi ventures to find his other half and when the gang enters Dartz's lair. 
In the manga, he returns unexpectedly by Yako Tenma, who revived him from the dead via "The Wicked Avatar", to gain information about Pegasus' death, since he was a competitor at Duelist Kingdom. Ultimately, Keith lies and says Yugi killed him, furthering Yako's thirst for revenge. This time around, he uses a new Machine Deck, composed of the "Motor" series, and the "The Wicked Eraser. He Duels and defeats Richie Merced, and took the one-of-the-kind black Duel Disk that only the top Card Professor was allowed to wear. Using the disk, however, forbid him from cheating due to a cheat-prevention installation. Keith found that out the hard way when he tried to sneak a "Ring of Destruction" from his wrist band.
He Dueled against Jonouchi once again. During this confrontation, Keith revealed that he hated Jonouchi as much as Pegasus, because of the defeat at Duelist Kingdom, and came back solely for revenge; having lost his chance to Duel against Pegasus (who died by the time Keith returned), Keith set his attention on the only other person who ever defeated him: Jonouchi. Unlike his anime counterpart's fate, who became too terrified of the so-called haunting to even notice Jonouchi, this manga counterpart became too obsessed with revenge against Jonouchi to notice Honda running past him, while not fearing about the dark magic involved. Ultimately, Keith lost partly because of the "Time Machine" card he left behind at the Kingdom that Jonouchi picked up, as well as Tributing the "The Wicked Eraser" because of him not truly liking that card for being too boring to win with it. Keith, consumed with rage angrily demands Jonouchi fight him again, however instead Jonouchi returned the "Time Machine" card, and offered Keith a chance for one more rematch when Keith lets go of the his grudge, and to fight him for fun. After the Duel with Jonouchi, Keith slumped up against the wall; collapsed. Ultimately, his final fate remains unknown.
As a professional Duelist, Keith has a large number of Decks which he keeps hidden inside of his jacket, consisting of several different Deck themes. During his time is Duelist Kingdom, he lends several cards to Bonz to fortify the young Duelist's Zombie Deck (including "Zanki" and "Crawling Dragon"), although Keith's Main Deck consists of all sorts of Machines. In his Duel with Yugi, he also uses rare and powerful cards provided by the Rare Hunters, including the legendary "Zera the Mant". Despite his reputation, he cheats by hiding cards in his wristband. Similarly, when he wears the Rare Hunter robes, a claw mechanism feeds cards directly to his hand. Because the Duelists are so far from each other when Dueling at an arena, Keith's opponents rarely realize he is cheating.
In the manga, his Deck remains more or less the same as in the anime, using Machine monsters to overwhelm his opponents. His other Deck themes, as he explained, includes Dragons and [[[Warrior]]s. His cheating tactics were the same as in the anime (aside from the claw mechanism, which was not shown in the manga), though as Battle Boxes were used instead of Duel Arenas, his opponents were much closer to see him cheat, though they still fail to see it.
In Yu-Gi-Oh! R, his Deck is based on Summoning high-powered cards, specifically "The Wicked Eraser", similarly to Yako Tenma's Deck. However, the main body of his Deck is composed of "Motor" cards. His cheating tactic, however, failed in his rematch against Jonouchi due to the black Duel Disk's cheat-prevention alarm.