Kōsei Hirota is a veteran Japanese actor and voice actor born on February 12, 1951, in Fukuoka Prefecture, Japan. He is affiliated with the theatrical group Engeki Shūdan En. Hirota began his professional training in 1974 at the Gendai Engeki Kyōkai Affiliated Drama School before joining the En Engeki Kenkyūjo in 1975. He became a full member of the Engeki Shūdan En theater group in 1979, establishing a career that spans both stage and voice acting.

Hirota is known for his deep baritone voice, which he often lends to mature, authoritative, and villainous characters in anime, video games, and foreign film dubbing. His extensive anime filmography includes a wide range of supporting and guest roles across numerous long-running series. He voiced Udai Taxim in the classic space western Cowboy Bebop. In the Digimon franchise, he portrayed Mercurimon in Digimon Savers (also known as Digimon Data Squad). He has also voiced Hack in One Piece, Gengorou Onabara in Bleach, Gosunkugi in Naruto, and Takiji Kuroido in Kill la Kill. Other notable roles include Genzō Gōda in Hakata Tonkotsu Ramens, Farmus in The Witch and the Beast, Ganimard (G. Lestrade) in Undead Murder Farce, Donovan in Farming Life in Another World, Alexandro Pecchino in King of Thorn, the Roboworld President in Redline, Arnold in Spice and Wolf II, Al Dile in Beast Saga, and Quoatl in Turn A Gundam. He also provided the narration for The Legend of the Condor Hero.

In the realm of video games, Hirota has provided the Japanese voices for several prominent characters. He voiced Blackbeard in the Japanese version of Assassin's Creed IV: Black Flag, Bael and Dagon in Devil May Cry 4, and Nightmare in the Soulcalibur series. In tokusatsu productions, he appeared as the voice of Bongan in Kaizoku Sentai Gokaiger.

Beyond animation and games, Hirota has an extensive career in dubbing foreign films and television series into Japanese. He is particularly known as the dedicated Japanese voice actor for the American actor Danny Trejo, dubbing his roles in films such as Machete, Spy Kids, Predators, and Breaking Bad. Other dubbing credits include Ron Perlman in films like Don't Look Up, Drive, and Nightmare Alley, as well as roles in Harry Potter and the Deathly Hallows Part 1, Ford v Ferrari, and Pirates of the Caribbean: On Stranger Tides.

On stage, Hirota has performed in theatrical productions of Shakespearean works, including Richard III, Macbeth, and Much Ado About Nothing, showcasing his versatility as a performer beyond voice work.