Gareth Armstrong is a British actor with a extensive career in theatre, television, and voice work, including contributions to English-language dubs of anime and animation. Born in Wales in 1948, he developed an early interest in acting, participating in school plays and joining the National Youth Theatre at sixteen before studying drama at Hull University.

His voice acting credits in animation and related genres include the role of Sandy in the BBC's famous English-language adaptation of the Japanese television series Monkey, based on the classic tale Journey to the West. He also provided the voice for the character Mephisto in the English version of the 1988 anime film Demon City Shinjuku. Beyond these projects, his voice work extends to video games, having lent his voice to titles such as Kameo: Elements of Power, Risen 2: Dark Waters, and games within the Warhammer franchise.

Armstrong is a regular guest artist with Big Finish Productions, contributing to their range of audio dramas. His long-standing partnership with this company represents a significant recurring collaboration in his audio career. He has also recorded an extensive number of audiobooks, including all seventy-five of the Maigret novels by Georges Simenon and novels for the Black Library, the audio branch of Warhammer.

Away from voice work, Armstrong has enjoyed a distinguished stage career, performing with the Royal Shakespeare Company and in London's West End. He is particularly known for his solo show Shylock, which he wrote and performed internationally for twenty-five years, earning awards and critical acclaim in multiple countries. He has also worked extensively as a director, teacher, and author, publishing books on his experiences in theatre. His contributions to radio were recognized with the Jewish Cultural Media Award for his work on the documentary The Blood Libel.