Sumi Shimamoto, born December 8, 1954, in Kochi Prefecture, Japan, is a highly respected Japanese actress, voice actress, and narrator. Her real name is Sumi Koshikawa. After graduating from the Toho Gakuen College of Drama and Music, she began her career with the theatrical troupe Gekidan Seinenza and is currently independent of any talent management company.

Shimamoto's voice acting debut came in 1979, and her career quickly gained prominence with her first major film role that same year as Clarisse in Hayao Miyazaki's Lupin III: The Castle of Cagliostro. This performance left a strong impression on Miyazaki, leading to her being cast as the titular heroine Nausicaä in the 1984 Studio Ghibli film Nausicaä of the Valley of the Wind. Her portrayal of Nausicaä is considered iconic, with a specific scene featuring a desperate scream being praised by critic Patrick Drazen as one that "tears at the listener and raises the bar for cartoon voices". This role cemented her status as a leading voice actress of the 1980s. She continued her association with Miyazaki and Studio Ghibli, voicing Yasuko Kusakabe, the mother, in My Neighbor Totoro (1988) and Toki in Princess Mononoke (1997).

Throughout the 1980s and 1990s, Shimamoto became known for her "water-like, crystal clear voice," often portraying gentle, noble, or pure-hearted characters. Some of her most celebrated roles from this period include the widow Kyoko Otonashi in the romantic comedy Maison Ikkoku (1986), the titular character in A Little Princess Sara (1985), and Dorothy in The Wonderful Wizard of Oz (1986). She also began her long-running role as Shokupanman in the enduringly popular children's series Soreike! Anpanman in 1988, a character she continues to voice. Her ability to portray a wide range of characters extended to more mature roles in the 1990s, such as the mysterious Ginrei in the Giant Robo OVA series and the glamorous former actress Yukiko Kudo, mother of the protagonist, in Detective Conan.

In her later career, Shimamoto successfully transitioned to playing motherly and matriarchal figures, a shift that helped popularize this archetype in anime. Notable roles include Kanata Izumi in Lucky Star (2007), Mitsuba Okita in Gin Tama (2007), and Royal Queen in Smile PreCure! (2012). Her film work continued with roles in Children Who Chase Lost Voices (2011) and a 2018 film in the Natsume's Book of Friends series. In the 2020s, she has continued to work steadily, with roles in series such as Dragon Goes House-Hunting (2021), Getter Robo Arc (2021), and Insect Land (2022).

Shimamoto's talent and enduring career have been recognized with numerous accolades. She was a top winner in Animage's Anime Grand Prix polls for female voice actors in 1984, 1987, and 1988. In 2017, she received the Kazue Takahashi Award at the 11th Seiyu Awards, which honors a voice actress for their long-standing contributions to the industry. Beyond performance, she has also contributed to the next generation as a lecturer at voice acting training schools. She is married to Daisuke Koshikawa, and their daughter, Shiori Koshikawa, has also become a voice actress.