Katsuji Mori is a veteran Japanese actor and voice actor born on July 10, 1945, in Tokyo, Japan. He began his career in entertainment as a child, initially through a children's theater troupe, and has remained active in the industry from the 1950s to the present day. His birth name is Miyuki Mori, and he was also known earlier in his career as Setsuya Tanaka. He later changed his registered name to Katsuji Mori.

Mori's career is deeply intertwined with the history of Japanese animation, particularly through his extensive work with Tatsunoko Production. He became renowned for voicing heroic and lead characters during the 1960s and 1970s, a period that established him as a quintessential protagonist voice actor. His breakthrough role came in 1967 as Go Mifune, the title character in Mach GoGoGo, known internationally as Speed Racer. He followed this by voicing Joe Shimamura, the cyborg 009, in the 1968 version of Cyborg 009. Perhaps his most iconic role from this era is Ken the Eagle, the leader of the Gatchaman team, in Science Ninja Team Gatchaman (1972) and its sequels Gatchaman II and Gatchaman Fighter. His portrayal of the stoic and capable leader became a defining performance of his career, a legacy he revisited decades later by voicing the character J.J. in the 2013 series Gatchaman Crowds. Other significant lead roles from this period include Jouji Minami, the titular hero in Tekkaman: The Space Knight (1975), and Naoto Date, the protagonist Tiger Mask, in the original 1969 Tiger Mask anime.

Throughout his long career, Mori has amassed an extensive and diverse filmography, taking on memorable roles in numerous major franchises. In the Mobile Suit Gundam universe, he is well-known as the voice of Garma Zabi, the young and earnest Zeon commander, a role he originated in the 1979 series and reprised in later film compilations and video games. He has also been a part of the Dragon Ball franchise, providing the voice for the Namekian warrior Nail in Dragon Ball Z. His role as the calculating and charismatic Nephrite in the first season of Pretty Soldier Sailor Moon (1992) is also a fan-favorite performance. In the 1990s OVA adaptation of JoJo's Bizarre Adventure, he voiced the French swordsman Jean Pierre Polnareff. More recently, he portrayed Professor Oak in the 2013 television special Pokémon Origins.

Mori's work extends across many other genres and series. He played Uchuuta Kamie in the pioneering super robot series Invincible Super Man Zambot 3 (1977) and was the voice of Wolfgang Mittermeyer in the epic space opera Legend of the Galactic Heroes and its films. He contributed to the Transformers franchise, voicing both the Autobot Metalhawk in Transformers: Super-God Masterforce and the Decepticon Weirdwolf in Transformers: The Headmasters. In the 1980s, he took on roles such as Victory Ramenman in Tatakae!! Ramenman and the villainous Shū in Fist of the North Star. He also voiced characters in series as varied as Dokaben, Armored Fleet Dairugger XV, Video Warrior Laserion, and Saint Seiya.

Beyond animation, Katsuji Mori has had a prolific career in dubbing foreign films and television series into Japanese. His notable dubbing roles include Horace Slughorn in the Harry Potter films, William Marshal in Robin Hood (2010), and characters in Mr. Robot and A Series of Unfortunate Events. He has also worked extensively as a narrator, including for the long-running Japanese morning show Mezamashi TV.

Throughout his career, Mori has frequently collaborated with a core group of fellow voice actors, appearing alongside them in numerous productions. Actors he has worked with repeatedly include Toshio Furukawa, Hirotaka Suzuoki, Banjo Ginga, and Toru Furuya, among many others. He was previously affiliated with Tokyo Actor's Consumer's Cooperative Society and later Aoni Production. He later became independent and founded his own talent agency, Office Mori, though the company eventually disbanded. He is currently represented by the agency plus one company.

In recognition of his long-standing contributions to the animation industry, particularly as a signature voice for Tatsunoko Productions, Katsuji Mori was a recipient of the Synergy Award at the 7th Seiyu Awards in 2013. His career, spanning over seven decades, solidifies his status as one of the foundational and most recognizable voices in Japanese anime history.