Ryūnosuke Yamaguchi is a Japanese voice actor born on June 17, 1992, in Tokyo, Japan. He is affiliated with the talent agency Atomic Monkey. Information about his early life and career beginnings is not widely available in English sources, but he has been active in the industry since at least 2020.

Yamaguchi is known for several supporting roles in anime productions. He made an early appearance providing additional voices for the 2021 film Gintama: The Very Final. His most prominent role to date is Hyota Sagara in the 2022 sports anime series Dance Dance Danseur, which focuses on a young boy's passion for classical ballet.

In 2023, Yamaguchi voiced the character Kabano in the fantasy adventure series Helck. That same year, he also had a role in the animated film Blue Giant, a story about three young jazz musicians in Tokyo. His first known credit is from 2020, where he played a minor role as a Sandwich Board Advertiser in the inventive series Keep Your Hands Off Eizouken.

The actor is the son of the very famous and prolific voice actor Kappei Yamaguchi, known for iconic roles such as Usopp in One Piece, Inuyasha, L in Death Note, and Shinichi Kudo in Case Closed. His sister, Akane Yamaguchi, is also a voice actor.