Voice actor Ken Yamaguchi was born under the name Kiyoshige Yamaguchi in Fukushima, Japan on March 24, 1956. While he was primarily known for being a voice actor, he also served as a sound director for the Spaceship Agga Ruter OVA in 1998. In addition, Yamaguchi also founded OYS Produce and Planning, a management agency for voice actors and actresses; the emphasis of the agency was on newcomers training in the field. Yamaguchi is also the father of anime voice actor Kiyohiro Yamaguchi.

Yamaguchi's voice acting career began in the 1970s. His first credit is Ippatsu Kanta-kun in 1977.

In the 1980s, Yamaguchi's work included Akama-kun, Armored Fleet Dairugger XV, the Crying Freeman OAV, Dragon Ball Z, Fist of the North Star, Fist of the North Star 2, the Good Morning Althea OAV, Guyver OAV, The Kabocha Wine, the Ladius OAV, the Legend of the Galactic Heroes OAV, Machine Robo: Revenge of Chronos, Machine Robo: The Running Battlehackers, the Madonna OAV, Manga Nihon Keizai Nyuumon, the Megazone 23 OAV, Musashi no Ken, the Project A-Ko film, the Riki-Oh OAV, the Saint Seiya series and film, the Sakigake!! Otoko Juku series and film, the Shonan Bakusozoku OAV, the Tatakae!! Rahmen Man series and film, Uchusen Sagittarius, three Violence Jack OAVs, and Wrestler Gundan Seisenshi Robin Jr.

Yamaguchi's voice acting roles in the 1990s included Bubblegum Crisis: Tokyo 2040, the Condition Green OAV, the Crayon Shin-chan: Action Kamen vs Haigure Mao anime film, the Dark Warrior OAV, the Doomed Megalopolis OAV, Dragon Ball GT, the Dragon Ball Z: The World's Strongest film, the Dragon Fist OVA, the Dragon Quest: Dai no Daiboken film and series, the Dragon Quest: Dai no Daiboken Buchiya bure!! Shinsei Rokudai Shoguo film, the Green Legend Ran OAV, Himitsu no Akko-chan, the Hyper Doll OAV, Karasu Tengu Kabuto, Kenyuu Densetsu Yaiba, Kikou Keisatsu Metal Jack, Kinkyuu Hasshin Saver Kids, Kinnikuman: Kinnikusei Oi Sodatsu-hen, Legendary Brave Da Garn, the Lightning Trap – Leina & Laika OAV, the Macross Dynamite 7 OAV, the Marmalade Boy series and movie, Matchless Raijin-Oh, Miracle Girls, the Ossu!! Karate Bu OAV, the Rennyo Monogatari film, the Riki-Oh 2: Horobi no Ko OAV, the Shiratori Reiko de Gozaimasu! OAV, the second Spirit Warrior OAV, the Street Fighter Alpha film, the Tottoi film, the Yamato 2520 OAV, and Yume no Crayon Oukoku.

In the 2000s, Yamaguchi could be heard in the Appleseed Ex Machina film, Black Lagoon, Casshern Sins, the Digimon Frontier Movie film, Digimon: Data Squad, Flag, Inuyasha, Kaleido Star, Lemon Angel Project, The Melody of Oblivion, Monster, Okusama wa Maho Shojo, PetoPeto-san, Rozen Maiden, Samurai Champloo, Sgt. Frog, Sonic X, and Zatch Bell.

Sadly, Ken Yamaguchi passed away on October 24, 2011 at the age of 55 due to illness.