Toshihiko Seki is a veteran Japanese actor, voice actor, and singer born on June 11, 1962, in Sendai, Japan. He has been active in the entertainment industry since 1983 and is affiliated with the talent agency 81 Produce. Recognized for his prolific output, Seki was noted as one of the more active male voice actors in the industry, with a significant number of roles to his name. In 2021, he was honored with the Kei Tomiyama Memorial Award at the 15th Seiyu Awards, which recognizes a voice actor for their body of work over a long period.

Seki is known for his versatility, portraying a wide range of characters across anime, video games, and tokusatsu productions. He has frequently voiced serious or easily agitated characters, but is equally skilled at playing composed individuals and deranged villains. Among his most iconic roles is the voice of Momotaros, an Imagin from the tokusatsu series Kamen Rider Den-O, a character he has reprised across numerous films and series. He is also well-known for his work in long-running anime franchises, such as Iruka Umino in Naruto, Duo Maxwell in Mobile Suit Gundam Wing, and Genjo Sanzo in the Saiyuki series.

His filmography includes leading and supporting roles in a vast array of series. He provided the voice for the sentient uniform Senketsu in Kill la Kill and the main antagonist Muzan Kibutsuji in Demon Slayer: Kimetsu no Yaiba. In the Gundam franchise, he has played multiple characters, including Rau Le Creuset in Mobile Suit Gundam SEED and Rey Za Burrel in Mobile Suit Gundam SEED Destiny. Other prominent roles include Duo Maxwell in Mobile Suit Gundam Wing, Musashi Goda in Mob Psycho 100, Kyosuke Irie in Higurashi: When They Cry, and Aleister Crowley in A Certain Magical Index. He has also lent his voice to numerous video games, such as Dissidia Final Fantasy as the Warrior of Light and Genshin Impact as Dottore.

Beyond animation, Seki's career encompasses narration, stage work, and music. For eight years, he hosted the NHK educational music program Fue wa Utau, where he was affectionately known as "Toshi-kun". His talent and longevity in the industry have made him a respected figure, inspiring younger voice actors such as Takahiro Sakurai to pursue the profession. In 2023, he starred as the titular character in the anime adaptation of Pluto.