Katsuya Jounouchi
"Yugi, I don't care if the person inside you is evil,
nor what evil things he does,
I swear, no matter what I will always be your friend."
Episode 24 Manga Volume 5
A freshman at Domino High and also Yugi's best friend. Jounouchi is a real tough guy but has a good heart. He cares very much about his friends and will do anything to help them, usually getting himself into trouble. When he first met Yugi he and Honda used to bully him. In the first story/episode Jounouchi stole a piece of the Millenium Puzzle, but that all changed when Yugi stood up against a stronger bully for him and considered themselves friends and Jounouchi later returned it to him.

(note: That was the first time Yami no Yugi appeared and scared the crap outta the bully)
Jounouchi cares very much about his little friend because he knows how easily he can get in trouble.
Honda and Jounouchi have been good friends since grade school, and are almost always hanging out together around the city. But never at Jounouchi' house because Jounouchi's father has been a drunken ass and will throw a beer bottle at you just for opening the door.
Jounouchi treasures his friendship with Yugi, and will follow him into any dangerous situation just to protect him.
When Jounouchi went with Yugi to Kaiba's Death-T Tornament, he proved his friendship with Yugi, when Yugi confessed to the group that he has know about another 'person' in his body since he completed the Millenium Puzzle, who has taken over from time to time, doing things unknown to Yugi. Yugi expected all his friends to leave him but Jounouchi said something everyone there could agree on.