Pierre the Gambler - known in Japan as Mitsuo (ミツオ) with the nickname Boy (ボーイ) - is Asuka (Alexis in the english version) childhood classmate who also happens to be world famous gambler having mastered games from blackjack to poker. Years ago, he stole Asuka's red handkerchief for beating him in a game of duel monsters. He duels Asuka in Duel Academy but loses. In the end, it is revealed he actually has a crush on Asuka and returns the handkerchief to her.

Source: Yu-Gi-Oh Wikia Entertainment