Kiyohiro Yamaguchi, also known by the stage name Kiyohiro Yamaguchi, is a Japanese actor and voice actor born on May 19, 1981, in Tokyo. He is the son of the late veteran voice actor Ken Yamaguchi, an influence that inspired his own career path from a young age after seeing his father's work. Yamaguchi began his career in the 1990s and has built a diverse portfolio spanning animation, video games, and stage performances.

Yamaguchi's voice acting career includes a wide range of roles in anime television series. He has appeared in productions such as Bleach, Future Diary, Detective Conan, The Promised Neverland, and The Millionaire Detective Balance: UNLIMITED. He is also known for his role as Prometheus in Wind -a breath of heart-. In the OVA adaptation of Dogura Magura, he voiced the character Sōta Amakasu. He also provided the voice for Jans in the 2018 television series Uchi no Oochopus.

In addition to television, Yamaguchi has contributed to original video animations and film. His film work includes roles in HELLS ANGELS and The Glacier Fox's Story. He also voiced a character in the 2024 web animation adaptation of Kimi ni Todoke. His work in video games is notable, including the lead role of Jack the Ripper in Murder Detective: Jack the Ripper. He has also lent his voice to the Japanese version of the 2024 video game Black Myth: Wukong, playing the character Sun Wukong.

A significant aspect of Yamaguchi's career is his continuation of his father's legacy. Following Ken Yamaguchi's death in 2011, he took over several roles his father had originated. The most prominent of these is the character Arinko Kid (Ant Kid) in the long-running children's series Soreike! Anpanman, a role he has performed since 2015, including in the film Soreike! Anpanman: Mija to Mahō no Lamp. He also inherited the role of Hosokawa in the Zatch Bell! game franchise.

Beyond acting, Yamaguchi has worked as a narrator for commercials and programs, and he remains active in stage theatre. Throughout his career, he has been affiliated with several talent agencies, including Doa Production and Sigma Seven e, before joining his current agency, SSP, in December 2019.