Kōichi Yamadera (山寺 宏一,Yamadera Kōichi) (June 17, 1961 - ) is a Japanese seiyū, actor, tarento, narrator, master of ceremonies and impressionist from Shiogama, Miyagi Prefecture. He graduated from Tohoku Gakuin University's economics school, and is currently affiliated with Across Entertainment. Before that, he was affiliated with the Tokyo Actor's Consumer's Cooperative Society.
His nickname is Yama-chan (山ちゃん,Yama-chan). As a radio personality, he is known as Bazooka Yamadera (バズーカ山寺,Bazūka Yamadera) among other things. He is best known for his roles in Kaiketsu Zorori (Zorori), the Japanese dub of Full House (Joey Gladstone), Ranma ½ (Ryōga Hibiki/P-chan, Jusenkyō Guide), Soreike! Anpanman (Cheese, Kabao, Kamameshidon), Brave Exkaiser (Osamu Tokuda), Ghost in the Shell (Togusa), Neon Genesis Evangelion (Ryōji Kaji), Cowboy Bebop (Spike Spiegel), the Yatterman remake (Narrator, Yatter-Wan, Odatebuta), and Mobile Suit Gundam: Char's Counterattack (Gyunei Guss). He is known for voicing Jim Carrey and Eddie Murphy in the Japanese language releases of their respective films.