Kōichi Nagano is a Japanese voice actor, born on December 12, 1966, in Sakura, Chiba Prefecture, Japan. Before fully committing to a career in voice acting, he worked at Tokyo Disneyland. He pursued his new dream by training at the Tokyo Announce Academy before joining the talent agency 81 Produce, where he laid the foundation for his career. He is known to have become a freelance voice actor, leaving 81 Produce in October 2004.

Nagano made his anime debut in 1990. He has portrayed a wide range of characters, often in supporting roles across many long-running anime series. He is most widely recognized for his role as Helmeppo in One Piece, a character who starts as the spoiled son of a corrupt Marine captain before undergoing significant personal growth and becoming a Marine himself. Nagano has voiced Helmeppo for over two decades, appearing in numerous episodes of the television series as well as several films, including One Piece Film: Z and One Piece Film: Red.

His other notable roles include Ryōkan Kurita, a gentle giant and offensive lineman for the Deimon Devil Bats, in the football anime Eyeshield 21. He also voiced Yuichiro Hikari, the father of the protagonist in the video game-based series MegaMan NT Warrior (Rockman EXE). In the Beyblade franchise, he portrayed the character Rai, which he has cited as a personal favorite role.

Nagano has contributed to many other well-known anime titles, often in guest or one-off capacities. His filmography includes roles in Neon Genesis Evangelion, where he played a minor character in the original series and in the first Rebuild film, as well as roles in Detective Conan, Hunter x Hunter (2011), The Prince of Tennis, and Katekyo Hitman Reborn!. He has also taken on roles in several original video animations (OVAs) and films. For example, he voiced Masaki Itō in the romance OVA With You ~Mitsumeteitai~ and the Superintendent in the sci-fi film The Asylum Session. In the MazinKaiser OVA series, he provided the voices for both Professor Sewashi and the character Mucha. He also contributed to the children's anime Baby Felix, voicing the characters Dog and Master Cylinder. Kōichi Nagano remains a working and respected voice actor in the industry, celebrated for his versatility and for bringing authenticity to a wide variety of characters over a career spanning more than three decades.