Koji Yamamoto is a Japanese actor and singer who was born in Tokyo on October 31, 1976. He began his career in entertainment as a child, working as a baby model from less than one year of age. His professional stage debut came at the age of ten when he played the role of Gavroche in the original Japanese production of the musical Les Misérables. He is widely recognized for his extensive work in television dramas, film, and particularly on the stage, where he has starred in numerous musical productions. His portrayal of the historical figure Hijikata Toshizō in the 2004 NHK大河剧 Shinsengumi! is considered a signature role and brought him significant fame. He has also appeared in films such as Shin Ultraman and the live-action Fullmetal Alchemist films.

In addition to his live-action work, Yamamoto has contributed his voice to animated projects. He is credited with the role of Hanazawa Rui in the 1996 anime television series adaptation of Hana Yori Dango (Boys Over Flowers), as well as its 1997 film counterpart. He also provided the voice for the character Torauma in the 2016 animated film Eiga Precure All Stars: Minna de Utau Kiseki no Mahō!.