Isao Natsuyagi was a Japanese actor and voice actor born on December 25, 1939, in Tokyo, Japan. He passed away on May 11, 2013. He began his career after studying at the Bungakuza actors school and later graduating from the Haiyuza actors school. He made his film debut in 1966 after joining the Toei studio. While Natsuyagi was primarily known for his extensive work in film and television, appearing in over one hundred films, his voice acting work, particularly in anime, represents a smaller but notable part of his career.

In the realm of anime, Natsuyagi is recognized for his role in the Kindaichi Case Files franchise, as mentioned in the prompt. He provided the voice for the character Isamu Kenmochi in the 1996 animated film The Kindaichi Case Files: The Opera House - A New Murder. He also had a guest role as a school teacher in the related television series The Kindaichi Case Files in 1997. Another significant voice role was as the narrator for the 1998 anime film Galaxy Express 999: Eternal Fantasy.

Beyond these specific roles, Natsuyagi's voice was also heard in Japanese dubs of foreign films. Notably, he dubbed the voice of Clint Eastwood in the films The Bridges of Madison County and A Fistful of Dollars, as well as Sylvester Stallone in Nighthawks. His career was marked by numerous accolades for his live-action performances, including winning the Best Actor award at the 67th Mainichi Film Award for his role in the 2012 film Land of Hope and receiving the Japan Academy Prize Chairman's Special Award in 2014.