Gansley

Gansley, known as Konosuke Oshita in the Japanese version, is the former vice-president of KaibaCorp and the leader as well as the founder of the Big Five.

Personality
Gansley is obsessed with business and as such refers to his monsters as employees. In the Japanese version, he quotes various warlords and philosophers on how to build a successful army. In the English dub, he gives Yugi Muto advice on business.

In the Japanese version, Gansley knows of Yami Yugi's existance and refers to Yugi as Type-A and Yami Yugi as Type-B Yugi. In the English version, Gansley shows no knowledge of Yami Yugi.

KaibaCorp
Gansley worked as vice-president of business strategy at KaibaCorp. Gansley, along with 4 other KaibaCorp employees form a group known as the Big Five.

Seto Kaiba, the adoptive son of the head of KaibaCorp, Gozaburo Kaiba, convinces the Big Five that Gozaburo is mistreating them and he'll help restore them to their former power. The Big Five agree, and thus buy 49% of KaibaCorp. Combined with 2% that Gozaburo had previously given to Seto for a test to prove his business skill, the Big Five vote out Gozaburo and vote in Seto as the president of the company.

Duelist Kingdom
However, Seto quickly backs out on their deal, stripping them of their power and leaving the Big Five little more than figureheads and consultants. Furious over their betrayal, the Big Five strike a deal with the president of Industrial Illusions, Maximillion Pegasus in an attempt to overthrow Seto. If Pegasus defeats Seto and Yugi Muto in duels, then they will use their 49% to vote Pegasus into power of the company by kidnapping Mokuba Kaiba, who has been entrusted with the security codes to the two percent the Big Five need.

The Big Five and Pegasus' plan fails, after Pegasus is defeated by Yugi. In the manga, Seto fires them for their betrayal.

Legendary Heroes
In the anime, the Big Five avoid being fired, by making excuses and offering Seto his complete virtual reality game as a peace offering.

Eager to try out the virtual reality game, Kaiba refrains from immediately firing them and enters the virtual world. The Big Five trap Kaiba in the virtual reality.

However Kaiba is rescued by Mokuba, Yugi, Joey Wheeler, and Mai Valentine. The Big Five reprogram the game and set the Mythic Dragon as the final boss. However it is defeated by Yugi and Kaiba's Dragon Master Knight.

Virtual Realm
After losing in Legendary Heroes, the Big Five got trapped in the virtual world, instead of Kaiba. Here they meet up with Noah Kaiba. Having Seto as a common enemy, they make plans to get revenge.

During the Battle City tournament, the Noah has the KaibaCorp blimp sucked into an undersea fortress, where the virtual world's main servers are. They force Seto and Mokuba Kaiba, along with Yugi and his friends into the virtual world again. Using an altered set of Duel Monsters rules, involving Deck Masters, the Big Five duel their enemies in the hopes of stealing their bodies to escape the virtual reality.

Gansley takes the form of Deepsea Warrior, which he uses as his Deck Master. He chooses to duel Yugi, and claims to have perfected a strategy to defeat him. As Yugi constructs a Deck, Gansley misinterprets Yugi saying "Kuriboh's" name, as him choosing Kuriboh as his Deck Master. He refuses to let Yugi change his Deck Master after that. Gansley manages to get the upperhand against Yami Yugi and is about to win, but Yugi takes control and uses "Kuriboh's" Deck Master effect to save them. Yami then uses "Kuriboh", combined with "Rainbow Blessing", allowing him to bypass Gansley's monsters and attack him directly with "Swift Gaia the Fierce Knight", defeating him.

Gansley, along with Crump, Johnson and Lector, having failed to win their targets bodies, go behind Noah's back and attempt to steal the bodies. They chase down Duke Devlin, Serenity Wheeler and Joey. As they argue over who gets which bodies, Noah makes contact and tells them off. Since Nesbitt didn't rightfully take Tristan Taylor's body, Noah allows the Big Five to share Tristan's body in order to Duel Yugi. Should they win, they would get their freedom.

The Big Five face Yugi and Joey, using Tristan's body. The 5, each switch control and Deck Master throughout the Duel. Gansley only takes full control for 1 turn. Towards the end of the Duel, the Big Five uses "Dragon Revival Ritual" to combine their Deck Masters into the Mythic Dragon, "Five-Headed Dragon" again. The dragon is destroyed by Yugi and Joey's "Mirage Knight", but the Big 5 use "A Deal with Dark Ruler" to make "Berserk Dragon" their Deck Master. However it is destroyed by "Dark Magician Knight", costing them the Duel.

Noah refused to give the Big Five any more chances after that and left them trapped in the Virtual World. They have not been seen since. Later, when the virtual world was destroyed, everyone inside it at the time was destroyed with it, including the Big Five.

Deck
Gansley uses a Reptile/WATER Deck that relies on Summoning many monsters to use the ability of his Deck Master "Deepsea Warrior", called "Reflector Hole" which negates an opposing attack and inflicts damage to the opponent equal to the attacking monster's ATK at a cost of two Tributes.