Masaki Aizawa is a Japanese voice actor, or seiyuu, born on January 19, 1965, in Hokkaido, Japan. He is currently affiliated with the talent management firm Office Osawa. Over the course of his career, he has also been represented by Production Baobab and Bell Production, and he once used the stage name Masaki Aizawa written with different kanji characters. Aizawa made his professional debut in 1983 and has since built a extensive and versatile portfolio spanning television anime, animated films, video games, and Japanese dubs of foreign films and television series.

Aizawa is known for his deep and commanding voice, which he has lent to a wide array of characters, often in action-oriented series. He frequently portrays powerful, imposing figures, whether they are heroes or villains. In the long-running franchise One Piece, he voices Wiper, a fierce warrior of the Shandia tribe from the Skypiea arc. He has multiple roles within the Naruto franchise, including Hanzaki in the original series and the voice of the tailed beast Gyūki in both Naruto: Shippuden and its sequel, Boruto: Naruto Next Generations. In the boxing anime Hajime no Ippo, he plays the role of Eiji Date, a former champion seeking to reclaim his title. He also voices Shouryuu in The Twelve Kingdoms and Zest in Magical Girl Lyrical Nanoha StrikerS.

Beyond these long-running series, Aizawa has taken on significant roles in numerous other productions. In the Pokémon anime, his most prominent roles have been the villainous team leaders: Ghetsis from Pokémon Black and White: Rival Destinies and Archie, the leader of Team Aqua, in the Advanced Generation series. He is also the voice of Sidney Sithole in The Legend of the Galactic Heroes: Die Neue These. His film work includes the role of Ralph Hardy Mirphak in The irregular at magic high school The Movie: The Girl Who Summons the Stars, Damian in the CG-animated film Resident Evil: Vendetta, and Yue-Shen in the acclaimed animated feature Sword of the Stranger. In the Death Note franchise, he voices Anthony Rester, a member of the SPK, in both the anime series and the compilation film Death Note Relight 2 - L's Successors. He has also appeared in Yu Yu Hakusho as Ōtake, in Bleach as Gunjo in the film Hell Verse, and as Chaos in The Erotic Temptress.

Aizawa is also highly active in the field of dubbing, providing the Japanese voice for international film and television actors such as Chow Yun-fat, Esai Morales, and Clark Gable. His work extends to narration for various television programs, documentaries, and even planetarium shows, and he has contributed to audio guides for visually impaired audiences. A lifelong fan of the band Queen, he was a drummer in a cover band during his high school years in Hokkaido.