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), 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.

山口胜平，日本著名声优、电台节目主持人、播音及舞台剧演员。现为二十一世纪霍士剧团成员之一。已婚，为纪念曾经参与乱马1/2的声优工作，将女儿取名为“山口茜”（与乱马1/2的天道茜同名）。主要作品有《海贼王》乌索普、《犬夜叉》犬夜叉、《死亡笔记》L、《名侦探柯南》工藤新一、《乱马1/2》早乙女乱马等。

山口勝平，日本男性配音員、演員。個人事務所悟空代表。兒子山口龍之介也從事配音工作。女兒山口茜從事配音兼落語工作。出身於福岡縣福岡市。