Bonz, known as "Ghost" Kotsuzuka in the Japanese version, "Ghost" Kozuka in the English manga and "Ghost" Bonz in the Singaporean dub of the anime, is one of Bandit Keith's former lackeys. Bonz's ghastly appearance is said to be caused by a glandular problem.
In the Duelist Kingdom tournament, he along with Sid and Zygor were Bandit Keith's henchmen after he agreed to share his expertise with the young Duelists so that all four of them would advance to the finals. Keith wanted revenge at Maximillion Pegasus for humiliating him in the final match of the Inter-Continental Championship. In secret, Keith merely wanted to use them for their Star Chips. Under Keith's tutelage, all three Duelists win Duels on the first day of the tournament, with Bonz at a total of four Star Chips. When Keith learned that Yugi Muto, Joey Wheeler, and their friends had entered the tournament as well, he believed they would impede them, and sought to eliminate them. Bandit Keith later found a secret Graveyard field, and chose Bonz to play in it because it suited his Ghost Deck. Because Keith was initially unimpressed by Bonz's Deck, he lent Bonz him some of his own cards to improve it, including his trump card, "Call of the Haunted".
Meanwhile, Sid and Zygor looked for Joey, believing him to be an amateur. When Joey ran away from the group towards a waterfall, Zygor beat him unconscious. Joey woke up in cave with a Dueling Arena, complete with a Graveyard field. Bonz challenged Joey to a Duel and tricked him into thinking that he must accept. Bonz had the upper hand, as his Zombie-Type monsters gained a 30% ATK bonus from the Graveyard Field, and when they were destroyed, they just regenerated, and gained ATK from "Call of the Haunted". However, when Yugi and their friends arrived, Joey managed to figure out the Zombies' main weakness; that their DEF is 0. Joey used "Shield and Sword" to switch their ATK and DEF values, and won the Duel. Bandit Keith then locked them in, beat up his three companions, took their remaining starchips, and entered the Duelist Kingdom Finals himself, having abandoned the three, saying that they had outlived their usefulness to him.
Bonz, along with Sid and Zygor were then seen right before the Battle City finals. The three stayed in a nearby cemetery and tricked people into giving up their Locator Cards. However, Yami Bakura was not intimidated by their act and challenged them to a Duel in which the winner takes all the Locator Cards, and thus may enter the Battle City Finals directly. Bonz had the advantage at first, but Bakura won quickly after. He then banished them to "Hell" (the Shadow Realm in the dub). It's unknown if they were ever released from their imprisonment.
Bonz (as Necromancer) plays a Zombie Deck. All his monsters are powered by the Wasteland terrain. His Deck Leader, "Pumpking the King of Ghosts" increases the ATK of all his Zombies near him by 500. The Pumpking in his Deck allows gives his monsters a 100 ATK boost each round.