Mari Yaguchi is a Japanese entertainer whose career spans singing, acting, and voice acting. Born on January 20, 1983, she first gained national prominence as a second-generation member of the popular idol group Morning Musume, which she joined in 1998. During her time with the group, she became a key figure within the Hello! Project collective, founding and leading the sub-unit Mini-Moni, which was uniquely composed of members who were 150 centimeters tall or shorter.

Her voice acting work is closely tied to her idol persona, particularly her involvement with Mini-Moni. She voiced a super-deformed version of herself named Yaguchi-san in the animated segments of the variety shows Mini Moni the TV and Mini Moni Yaru no da Pyon!. This connection extended to other children's media; she and other Mini-Moni members voiced hamster characters called "Mini-Hamus" in the Tottoko Hamtarō film series, with her specific hamster counterpart named Gucchan.

Beyond roles based on her public image, Yaguchi contributed her voice to other major anime franchises. She provided the voice for the character Yoko in the long-running series One Piece and also sang the opening theme song Kaze o Sagashite for the franchise as part of the unit Mari Yaguchi with Straw Hat. She made a guest appearance as herself in the animated film Futari wa Precure Max Heart 2: Yukizora no Tomodachi.

A notable achievement in her voice acting career came from her personal passion for anime. In 2011, Yaguchi designed a new character named Panbachimon for the series Digimon Xros Wars, a half-panda, half-bee creature. She also provided the character's voice, an opportunity she pursued as a self-proclaimed anime fan who wanted to try voice acting. Her career has also included live-action acting roles in dramas such as Gal Circle and stage productions like Damn Yankees. After a period of hiatus in 2013, she has since returned to making public appearances.