Koike, along with artist Goseki Kojima, made the manga Kozure Okami (Lone Wolf and Cub), and Koike also contributed to the scripts for the 1970s film adaptations of the series, which starred famous Japanese actor Tomisaburo Wakayama. Koike and Kojima became known as the "Golden Duo" because of the success of Lone Wolf and Cub.
Kazuo Koike started the Gekika Sonjuku, a college course meant to teach people how to be mangaka.
Graduates of Koike's Gekika Sonjuku
Notable graduates include:
- Rumiko Takahashi - manga artist: Ranma ½, InuYasha, Urusei Yatsura, etc
- Akira Sakuma - game designer, freelance writer: Momotetsu series
- Hideyuki Kikuchi - horror writer
- Tetsuo Hara - manga artist: Fist of the North Star
- Yuji Horii - game designer, freelance writer: Dragon Quest series
- Keisuke Itagaki - manga artist: Baki the Grappler
- Naoki Yamamoto - manga artist: Dance Till Tomorrow
Comics work includes:
- Lone Wolf and Cub, with artist Goseki Kojima, 1970–1976
- Hulk: The Manga, with artist Yoshihiro Morifuji, 1970–?
- Lady Snowblood, with artist Kazuo Kamimura, 1972–1973
- Samurai Executioner, with artist Goseki Kojima, 1972–1976
- The script to the film Lady Snowblood, 1973
- Adolescent Zoo, with artist Hiromi Yamasaki, 1978–1981
- Path of the Assassin, with artist Goseki Kojima, 1978–1984
- Mad Bull 34, with artist Noriyoshi Inoue, 1985–1991
- Crying Freeman, with artist Ryoichi Ikegami, 1986–1988
- Hannape Bazooka, with artist Go Nagai
- Kajō, with artist Hideki Mori, 2003–2006
- Yume Genji Tsurugi no Saimon, with artist Natsuki Sumeragi, 2006–?
- Shura Yukihime Gaiden, with artist Ryoichi Ikegami, 2009-?
- Oda Nobunaga, with artist Goseki Kojima, ?-?
- Kawaite Sourou, with artist Goseki Kojima, ?-?
- Offered, with artist Ryoichi Ikegami, ?-?