Isamu Tanonaka was a Japanese actor and voice actor born on July 19, 1932, in Taitō, Tokyo. He began his career affiliated with Gekidan Tōgei and later Theatre Echo before joining Aoni Production, the agency he was with at the time of his death. Despite having a naturally deep voice, he became famous for portraying characters with a high-pitched voice. He passed away on January 13, 2010, from a heart attack at the age of 77.

Tanonaka's most iconic and enduring role was as Medama Oyaji, the anthropomorphic eyeball and father of the title character in the long-running franchise GeGeGe no Kitarō. He first voiced the character in the initial 1968 anime adaptation and continued in the 1971 follow-up series. When production began on a new series in the 1980s, the plan was for a completely new cast, but after auditions failed to find a suitable replacement for Medama Oyaji, Tanonaka was asked to reprise the role. From that point on, he voiced the character in nearly every adaptation of Shigeru Mizuki's work made during his lifetime, including five different anime television series, numerous theatrical films, live-action films, commercials, and variety show appearances. In 2008, he reunited with his long-time co-stars Masako Nozawa and Chikao Ōtsuka to reprise their original roles for the darker series Hakaba Kitarō. His 41-year association with the role made him the definitive voice of the character.

Another significant role in his later career was Igor, the master of the Velvet Room, in the Persona series of video games and their animated adaptations. He voiced the character in Persona 3 and Persona 4, as well as in the Persona 3 movies, Persona: Trinity Soul, and the Persona 4 animations. Following his death in 2010, his previously recorded lines were used for Igor's appearances in subsequent works like Persona 4: The Animation, Persona 4 Arena, and even for the appearance of the real Igor in Persona 5, serving as a lasting tribute to his performance.

Beyond these defining roles, Tanonaka had a prolific career with many other notable performances. He was the first voice of Honkan-san in Tensai Bakabon. He voiced multiple characters in the Dr. Slump & Arale-chan series, including Gara and a character named after Akira Toriyama. In the Mazinger Z franchise, he played the roles of Mucha and Dr. Nossori. His other prominent anime roles included Sindbook in Magical Princess Minky Momo, Youaltepuztli in Akuma-kun, Brass in Dragon Quest: Dai no Daibōken, and Shōjō in One Piece. He also contributed his voice to numerous foreign language dubs, most notably as Jar Jar Binks in the Japanese-language versions of Star Wars: Episode I – The Phantom Menace and Star Wars: Episode II – Attack of the Clones. His final performance was as Leonardo da Vinci in the anime series Marie & Gali.