JAPANESE VOICE ACTOR: Hiroaki Hirata
Klein, whose real name is Ryōtarō Tsuboi, is voiced by Hiroaki Hirata in the Japanese version of Sword Art Online. As Kirito’s first friend inside the death game of Aincrad and the leader of the guild Fuurinkazan, Klein quickly became one of the franchise’s most recognizable supporting characters. Hirata’s charismatic and energetic performance helped define Klein’s loyal, humorous, and dependable personality.
Date of Birth
August 7, 1963.
About Hiroaki
Hiroaki Hirata is a Japanese actor, narrator, and voice actor with a career spanning decades across anime, video games, film dubbing, and theater. He is especially famous for voicing Sanji in One Piece, but anime fans also recognize him as the voice behind several iconic heroes, mentors, and swordsmen. His portrayal of Klein brought warmth and humor to Sword Art Online while maintaining the character’s reliability during the series’ most dangerous moments.
Hometown
Tokyo, Japan.
Career Highlights
- Klein / Ryōtarō Tsuboi — Sword Art Online
- Sanji — One Piece
- Kotetsu T. Kaburagi / Wild Tiger — Tiger & Bunny
- Vergil — Devil May Cry
- Mutta Nanba — Space Brothers
- Leomon — Digimon Adventure
- Balthier — Final Fantasy XII
Full Current Filmography
The following reflects documented major credits and may not be exhaustive.
Television Anime
- Sword Art Online — Klein / Ryōtarō Tsuboi
- Sword Art Online II — Klein
- Sword Art Online: Alicization — Klein
- One Piece — Sanji
- Tiger & Bunny — Kotetsu T. Kaburagi
- Space Brothers — Mutta Nanba
- Saiyuki — Sha Gojyo
- Digimon Adventure — Leomon
Anime Films
- Sword Art Online The Movie: Ordinal Scale — Klein
- Sword Art Online Progressive: Aria of a Starless Night — Klein
- Various One Piece films — Sanji
- Multiple Tiger & Bunny film projects — Kotetsu T. Kaburagi
Video Games
- Sword Art Online: Infinity Moment — Klein
- Sword Art Online: Hollow Fragment — Klein
- Sword Art Online: Hollow Realization — Klein
- Sword Art Online: Last Recollection — Klein
- Sword Art Online: Fractured Daydream — Klein
- Devil May Cry series — Vergil
- Final Fantasy XII — Balthier
Critical Reception
Fans frequently praise Hiroaki Hirata’s performance for making Klein feel like the most grounded member of Kirito’s friend group. His comedic timing, natural delivery, and emotional sincerity helped establish Klein as one of the franchise’s most dependable and likable characters.
Our Sources
- Behind The Voice Actors — Klein / Ryotaro Tsuboi Voices (https://www.behindthevoiceactors.com/characters/Sword-Art-Online/Klein-Ryotaro-Tsuboi/)
- Behind The Voice Actors — Sword Art Online TV Cast (https://www.behindthevoiceactors.com/tv-shows/Sword-Art-Online/Klein-Ryotaro-Tsuboi/)
- Wikipedia — Hiroaki Hirata (https://en.wikipedia.org/wiki/Hiroaki_Hirata)
- AniBase — Klein Character Profile (https://anibase.net/en/character/lVVEV/Klein)
ENGLISH VOICE ACTOR: Kirk Thornton
In the English dub of Sword Art Online, Klein is voiced by Kirk Thornton. His performance captures Klein’s mix of confidence, humor, loyalty, and occasional recklessness, making him one of the most memorable members of the English cast. Thornton has portrayed Klein across the television series, films, and multiple video game adaptations.
Date of Birth
May 13, 1956.
About Kirk
Kirk Thornton is an American voice actor, ADR director, and screenwriter with one of the largest anime dubbing résumés in the industry. Since the 1980s, he has voiced hundreds of characters across anime, animation, and video games. His portrayal of Klein remains one of his most recognized anime performances.
Hometown
Portland, Oregon, United States.
Career Highlights
- Klein / Ryōtarō Tsuboi — Sword Art Online
- Shadow the Hedgehog — Sonic the Hedgehog
- Saïx — Kingdom Hearts
- Hajime Saitō — Rurouni Kenshin
- Jin — Samurai Champloo
- Shukaku — Naruto Shippuden
- Hotohori — Fushigi Yūgi
Full Current Filmography
The following reflects documented major credits and may not be exhaustive.
Anime Series
- Sword Art Online — Klein / Ryōtarō Tsuboi
- Sword Art Online II — Klein
- Sword Art Online: Alicization — Klein
- Samurai Champloo — Jin
- Naruto Shippuden — Shukaku, Fukasaku
- Blue Exorcist — Shiro Fujimoto
- Bobobo-bo Bo-bobo — Don Patch
- Gungrave — Brandon Heat
Anime Films
- Sword Art Online The Movie: Ordinal Scale — Klein
- Sword Art Online Progressive: Aria of a Starless Night — Klein
- Perfect Blue — English Dub Cast
- Ghost in the Shell — English Dub Cast
- Ninja Scroll — English Dub Cast
Video Games
- Sonic the Hedgehog franchise — Shadow the Hedgehog, Orbot
- Kingdom Hearts series — Saïx
- World of Warcraft — Various Roles
- Sword Art Online game franchise — Klein
- Multiple anime and RPG titles as actor and voice director.
Critical Reception
Kirk Thornton’s portrayal of Klein has been praised for bringing humor and veteran confidence to the character without losing the emotional sincerity that makes Klein such an important ally to Kirito. Many English dub fans consider him one of the standout supporting performances in the Sword Art Online franchise.
Our Sources
- Behind The Voice Actors — Klein / Ryotaro Tsuboi Voice Cast (https://www.behindthevoiceactors.com/tv-shows/Sword-Art-Online/Klein-Ryotaro-Tsuboi/)
- Behind The Voice Actors — Klein Voices (https://www.behindthevoiceactors.com/characters/Sword-Art-Online/Klein-Ryotaro-Tsuboi/)
- IMDb — Kirk Thornton Profile (https://www.imdb.com/name/nm0861558/)
- Wikipedia — Kirk Thornton (https://en.wikipedia.org/wiki/Kirk_Thornton)
