Years ago, the fearsome Pirate King, Gol D. Roger was executed leaving a huge pile of treasure and the famous "One Piece" behind. Whoever claims the "One Piece" will be named the new King of the Pirates. Monkey D. Luffy, a boy who consumed a "Devil Fruit," decides to follow in the footsteps of his idol, the pirate Shanks, and find the One Piece. It helps, of course, that his body has the properties of rubber and that he's surrounded by a bevy of skilled fighters and thieves to help him along the way. Luffy will do anything to get the One Piece and become King of the Pirates!
Mitsuo Yamaguchi (山口 光雄, Yamaguchi Mitsuo), better known by his stage name of Kappei Yamaguchi (山口 勝平, Yamaguchi Kappei) is a Japanese voice actor and actor from Fukuoka, affiliated with Gokū and 21st Century Fox. He is best known for the roles of Ranma Saotome (Ranma ½), Jackson Neil (Miracle Girls), Tombo (Kiki's Delivery Service), Yattaro (Kyattou Ninden Teyandee), InuYasha (InuYasha), Ryuichi Sakuma (Gravitation), L (Death Note), Usopp (One Piece), Hideyoshi (Law of Ueki), and Kaito Kid and Shinichi Kudo (Case Closed). His current starring roles include that of Raimon "Monta" Taro, the Deimon Devil Bats' ace receiver in Eyeshield 21. Yamaguchi has appeared in eroge as Kyōya Ushihisa (牛久 京也, Ushihisa Kyōya). He made his first public appearance in North America at Otakon 2008; and was also a guest at Sakura-Con 2009. Yamaguchi's third appearance to date has been at Animazement in 2010. He is married and has a daughter, Akane Yamaguchi (山口 茜), and a son, Ryunosuke Yamaguchi (山口 竜之介), who also are voice actors. Description above from the Wikipedia article Kappei Yamaguchi, licensed under CC-BY-SA, full list of contributors on Wikipedia.