Tomoko Yamaguchi is a Japanese actress and voice actress born on October 20, 1964, in Tochigi, Japan. While she is widely recognized for her leading roles in live-action television dramas, particularly the classic series Long Vacation, her career also includes notable work in animated films.

Yamaguchi's involvement in anime includes the 1993 film Coo: Tōi Umi kara Kita Coo, produced by Toei Animation, in which she provided the voice for the character Cassie Nozaki, also known as Cathy Nozaki. Years later, she took on a significant voice role in the highly acclaimed Studio Ghibli film Ponyo on the Cliff by the Sea, directed by Hayao Miyazaki and released in 2008. In Ponyo, she voiced Risa, the energetic and caring mother of the young protagonist, Sōsuke. Her performance as Risa is part of a voice cast that included other established figures from Japanese stage, film, and television.

In addition to her work in original Japanese animation, Yamaguchi has also contributed to Japanese dubs of foreign films. For instance, she voiced the character Mrs. Coulter in the Japanese-language version of the film The Golden Compass.

Yamaguchi's career in entertainment has been recognized with industry awards. In 1995, she was a recipient of the Elan d'or Award for Newcomer of the Year, an honor presented by the All Nippon Producers Association. Her on-screen career, which began in the mid-1980s, has seen periods of high activity, with a hiatus between 1996 and 2012 before she returned to acting.