Motoi Koyanagi is a Japanese actor and voice actor born on January 4, 1960. He is affiliated with the talent agency Remax. While some sources list his birthplace as Tokyo, others indicate he is from Hokkaido. He studied at Toho Gakuen College of Drama and Music but did not complete his degree.

Koyanagi's career began in experimental theater, where he was a member of renowned troupes such as Tenjo Sajiki, founded by Shuji Terayama, and Teatro Kai. He transitioned into voice acting and on-screen acting in the 1980s, building a career that has spanned several decades. His voice is recognized for its versatility, often portraying reliable elder figures, comedic side characters, or tough individuals.

He has accumulated numerous voice roles in anime television series. One of his notable ongoing roles is as Tomio Tamura, also known as Tommy, in the long-running series Prince Mackaroo, where he took over the part from the original actor. Other significant anime credits include Shigeru Sugie in SHIROBAKO, a character who is a veteran animator; John McEnroe in Death Note; Gunzo in Shigurui: Death Frenzy; and various characters in Gintama. He has also held roles in series like Kaiji, One Outs, Black Lagoon, and Revenger. His film work includes roles in the animated movie FLCL and the 2020 film SHIROBAKO the Movie.

Beyond anime, Koyanagi is active in video game voice acting, with credits including Bernhardt in Langrisser I & II and a role in Armored Core VI: Fires of Rubicon. He also works extensively in dubbing foreign films and television dramas for Japanese audiences, as well as narration for commercials and documentaries. His live-action acting credits include appearances in the films JUSO and JUNEN.