Koichi Yamadera was born on June 17, 1961 in Shiogama, Japan. He's a graduate of Tohoku Gakuin University & is affiliated w/ Across Entertainment. He's a prolific voice actor that specializes in video games, & TV animation.

His voice-acting debut was in the OVA Megazone 23 as the motorcycle-riding Shinji Nakagawa, while his TV debut was the anime Bosco Adventure as the cowardly but friendly otter. His break-out voice role was Ranma 1/2, in which he played Ryoga Hibiki & the Jusenkyo Guide. That same year, he voiced Shaman in the TV series Granzort. In 1991, he joined forces w/ Toshihiko Seki & Noriko Hidaka to form the acting unit Banana Fritters, which disbanded in 1995.

In October 1997, he became a host on the TV Tokyo children's variety show Oha Suta. In 1994, he married Mika Kanai. They divorced in spring 2006.

He's best known for his roles in Kaiketsu Zorori, the Japanese dub of Full House, Ranma 1/2, Soreike! Anpanman, Brave Exkaiser, Ghost in the Shell, Ghost in the Shell: Innocence , Neon Genesis Evangelion, Cowboy Bebop, the Yatterman remake, Mobile Suit Gundam: Char's Counterattack, Paprika & Vampire Hunter D-Bloodlust.

He's also known for dubbing for Jim Carrey & Eddie Murphy in English-language films.