Koji Ishii is a veteran Japanese voice actor and narrator born on July 1, 1960, in Wakayama Prefecture. He began his entertainment career with aspirations of being an on-screen actor, training at the Mifune Geijutsu Gakuin and performing on stage. His entry into voice acting occurred in 1988 when a connection with fellow voice actor Akira Kamiya led to him observing a recording session for the anime City Hunter 2, after which he was invited to participate in minor roles for the same series. Since that debut, Ishii has built an extensive and prolific career across anime, video games, narration, and dubbing for foreign films and television series. He is currently a freelancer with a business partnership with Ambernote, and has been previously affiliated with Ken Production, Kōya 25-ji, and Vi-vo.

Ishii's voice is characterized by a resonant low pitch that makes him a frequent choice for authoritative, powerful, or villainous characters, though he has also portrayed comedic and earnest roles. His career encompasses a vast range of roles, including those specified by the user. In anime, he has voiced Gaston in Hortensia Saga, Gregory Camelot in Hatena Illusion, Renjiro Hatonami in Gibiate, Teijirō Akizuki in Shine on! Bakumatsu Bad Boys, and a character in Kingdom. He also played Dim in Kikansha Yaemon and Inspector Ginzo Nakamori in the film Case Closed: The Fist of Blue Sapphire. Other credits include the role of Ulysses S. Grant in The Empire of Corpses, Goblin Suzuki in Demon Warrior Koji, Yanagi in Goal FH, and Guérin in TO. His work as a narrator is prominent in series such as Terraformars: Chikyū-hen, and he has also voiced Detective Yamazaki in the Finder Series.

Beyond these, Ishii is widely recognized for several signature roles. He is known for his performances as Koutaro Taiga in The King of Braves GaoGaiGar, the teacher Kimura in Azumanga Daioh, Garterbelt in Panty & Stocking with Garterbelt, Fisher Tiger in One Piece, Silva Zoldyck in the 1999 Hunter × Hunter series, and Prime Minister Honest in Akame ga Kill!. He has also been the second voice actor for characters like Inspector Ginzo Nakamori in the Detective Conan series and Tetsumaru Kinoshita in Nintama Rantaro.

Ishii has a significant presence in the video game world, with recurring roles in major franchises. He is particularly well-known as the voice of Ryuji Yamazaki, Sokaku Mochizuki, and Gato from the Fatal Fury and The King of Fighters series. Other notable game roles include Waldstein in the Under Night In-Birth series, Giovanni in Pokémon Masters, and Hisahide Matsunaga in the Samurai Warriors series.

His work also extensively covers foreign language dubbing. He has provided the Japanese voice for animated characters such as Mojo Jojo in The Powerpuff Girls, Kowalski in The Penguins of Madagascar, Yosemite Sam in The Looney Tunes Show, and the title character in The Pink Panther. In live-action dubbing, he is known for voicing characters played by actors like Samuel L. Jackson and Willem Dafoe. Additionally, Ishii is an accomplished narrator for a wide variety of television programs, including news shows like NEWS23 and Mezamashi TV, as well as documentaries. His career also extends to tokusatsu, where he voiced the character Damaras in Kaizoku Sentai Gokaiger.