Naoko Matsui is a Japanese voice actress and narrator born on April 4, 1961, in Hakodate, Hokkaido. She began her career in 1983 with a minor role in the anime Space Cobra and made her debut as a lead voice actress in 1985, voicing the title character in the original video animation (OVA) series Dream Hunter Rem. Her early career also included notable roles such as Uru Chie in High School! Kimengumi in 1985 and Roux Louka in Mobile Suit Gundam ZZ in 1986.

Matsui is widely recognized for her long-standing role as Sonoko Suzuki in the Detective Conan (Case Closed) franchise, a character she has voiced since 1996 across the television series, numerous films, and specials. Her filmography spans a wide range of genres and includes significant roles such as Chiyoko Wato in The Three-Eyed One, Katsumi Liqueur in Silent Möbius, Dorothy Catalonia in Mobile Suit Gundam Wing, Run Run in Mahōjin Guru Guru, and Rem Ayanokōji in the Dream Hunter Rem series. She has also appeared in popular series like Ranma ½ as Azusa Shiratori, Death Note as Naomi Misora, and Naruto as Yoshino Nara. In the 2010s, she voiced Ribbon in HappinessCharge PreCure!.

Her voice is characterized as a strong and high soprano, which has made her a frequent choice for assertive female characters and villains. Matsui was a member of Production Baobab for over 20 years before becoming a freelancer. In 2013, she founded her own agency, Up and Ups. Beyond voice acting, she is also a theatre actress and an instructor, having taught at the AMUSEMENT MEDIA綜合学院 and running her own voice training workshop, "Expression Academy". In 2015, she formed the unit "backdrops" with fellow voice actresses Noriko Hidaka and Wakana Yamazaki.