Ayumu Saitô is a Japanese actor, voice actor, playwright, director, and theatre producer born on December 20, 1964 in Hokkaido, Japan. While his career encompasses extensive work in live-action film and television, he is known to international audiences primarily for his voice role in anime.

Saitô is best known for providing the voice of Wabisuke Jinnouchi in the acclaimed 2009 animated film Summer Wars. In the film, he voices the character of the great-uncle of the main heroine, Natsuki Shinohara, a black sheep family member whose actions are central to the film's plot. He participated in an interview for the film's DVD release, discussing his role.

Beyond this prominent anime role, Saitô has built a substantial career as a live-action actor, appearing in numerous Japanese television dramas and films. His filmography includes roles in movies such as Ju-on: The Grudge 2 (2003), the live-action adaptation of Ace Attorney (2012), Crows Zero (2007), and the historical drama 13 Assassins (2010). On television, he has appeared in series including Bloody Monday (2008) and the long-running drama Aibō.

In addition to his on-screen work, Ayumu Saitô is an established figure in Japanese theatre. His primary occupation is as a playwright, director, and theatre producer, and he is represented by the agency Knockout. He has adapted and directed numerous stage productions, including works by William Shakespeare and Anton Chekhov, and has written his own plays such as Fuyu no Bayer and Saisen 11-jō no Aria. He also serves as the director of the Japan Directors Association.