Katsuya Jonouchi (Joey Wheeler) along with his friend Hiroto Honda used to bully Yugi in school. He said his bullying of Yugi was to make him a man, being annoyed with how Yugi would get pushed around and wouldn't fight back. He steals a piece of Yugi's puzzle and tosses it into the school pool. Yugi tried to stop another student from beating up Jonouchi and Honda which got him beat up in the process.
Feeling bad and inspired with how brave Yugi was Jonouchi retrieve the piece of the puzzle he tossed away. He returns it to Yugi's grandfather and the next day at school answers a riddle Yugi gave; "Something that you see, but have never seen before." that it's friendship and that he is Yugi's friend. This was the start of a great friendship between him and Yugi. Jonouchi would go on to prove his friendship to Yugi time and time over again, and visa versa.
Jonouchi's parents are divorced, and he is separated from his sister, Shizuka (Serenity in the English dub). He lives with his drunk, abusive father.
Jonouchi is a source of constant support for Yugi, he is always there to encourage his friend and even duel by his side on many occasions. Through Yugi and his grandpa's teachings Jonouchi has become an extremely skilled duelist, coming in second place in Duelist Kingdom. The only duelist he has never been able to defeat, that has challenged him, is Seto Kaiba who knows how to push Jonouchi's buttons.
Jonouchi can sometimes be quick to act, always leaping before he thinks. Sometimes is emotions can get the best of him, but with Yugi's help and his friends he overcomes them.
Normal Monsters - Alligator Sword, Axe Raider, Baby Dragon, Red Eyes Black Dragon, Swordsman of Landstar
Effect Monsters - Blue Flame Swordsman, Copycat, Gearfried the Iron Knight, Goblin Attak Force, Jinzo Lava Battleguard, Panther Warrior, Red Eyes Black Metal Dragon, Rocket Warrior, Swamp Battleguard, Sword Hunter, Time Wizard
Fusion Monsters - Alligator Sword Dragon, Black Skull Dragon, Dark Flare Knight, Flame Swordsman, Giltia the D. Knight Thousand Dragon
Spell Cards - Graceful Dice, Salamandra, Scapegoat, Shield and Sword
Trap Cards - Giant Trunade, Graverobber, Kunai with Chain, Magic Arm Shield, Skull Dice