Kazuo Koike was a Japanese manga writer, novelist, screenwriter, and entrepreneur, born on May 8, 1936, in Daisen, Akita Prefecture, and passed away on April 17, 2019, due to pneumonia. He was a prolific creator best known for his work as a gensakusha, or original writer, a role in which he provided the stories and concepts for manga that were then illustrated by collaborating artists. Early in his career, Koike studied under Takao Saito, the creator of the long-running series Golgo 13, and began working as a writer on Saito's productions in 1968.

Koike is most renowned for a series of violent and artistically ambitious seinen manga, which are titles aimed at adult men. His most famous work is Lone Wolf and Cub, created with artist Goseki Kojima and serialized from 1970 to 1976. This series, about a disgraced executioner who wanders feudal Japan as an assassin with his young son, became a landmark title. The success of this collaboration led to Koike and Kojima being known as the "Golden Duo". Other major works from this period include Lady Snowblood (1972-1973) with artist Kazuo Kamimura, about a woman born for vengeance, and Samurai Executioner (1972-1976), another collaboration with Kojima.

Throughout the 1980s, Koike continued to produce influential series. He wrote Crying Freeman (1986-1988) with artist Ryoichi Ikegami, a modern-day story of an assassin marked by his involuntary tears. He also collaborated with legendary artist Go Nagai on the manga Hanappe Bazooka, which was serialized in Weekly Shonen Jump from June 1979 to January 1982. This story follows a lecherous high school boy who gains strange powers after two demons emerge from a pornographic videotape. The manga was later adapted into a single-episode original video animation (OVA) released on September 4, 1992.

Another of Koike's works adapted into an anime is Itoshi no Betty Mamonogatari, a film released on July 19, 1986. This story follows a gangster who falls in love with Betty Valentine, a witch from a demon realm who has come to Earth seeking revenge for her sister's murder. For this production, Koike is credited as both the original creator and the director. The film is based on a manga, Mamonogatari Itoshi no Betty, which Koike wrote with artist Seisaku Kano. In addition to his more famous violent and erotic works, Koike, an avid golfer and former professional mahjong player, also wrote manga in those genres.

The themes in Koike's work are characterized by hyper-violence, meticulously choreographed action, and a deep exploration of personal honor and existential codes. His protagonists often operate under a strict moral code that puts them in conflict with societal laws. Sexuality and eroticism are also frequent elements in his narratives. Beyond entertainment, his work often contained a spirit of social critique, featuring anti-heroes who violently rebel against corrupt systems of power, a reflection of the protest-heavy atmosphere of 1970s Japan.

Kazuo Koike's significance to the manga and anime industry is substantial. His major series, along with their numerous adaptations into live-action films and other media, have been credited with influencing the international growth of Japanese popular culture. For example, a 1995 live-action film adaptation of Crying Freeman was directed by French filmmaker Christophe Gans. In 2004, Koike was inducted into the Will Eisner Comic Book Hall of Fame for his lifetime of achievements.

Beyond his creative work, Koike was a major educator and entrepreneur. In 1977, he founded Gekiga Sonjuku, a vocational school in Tokyo designed to teach aspiring manga artists, writers, and screenwriters. His pedagogy focused on the belief that compelling character creation is the foundation of storytelling. The school produced a generation of highly successful creators, including Rumiko Takahashi (Urusei Yatsura, Inuyasha), Yuji Horii (Dragon Quest), Tetsuo Hara (Fist of the North Star), and Hideyuki Kikuchi (Vampire Hunter D).