Ryoichi Ikegami saw his first short comic published in the magazine Garo. This comic was noticed by Shigeru Mizuki, who took Ikegami as his assistant. He started his first series, a western trilogy, at age 24. Success came in 1973 when he took on the series 'Aiueo Boy', along with scenarist Kazuo Koike. Two of this series, both published by Shôgakukan, were introduced on the American market in 1987 and 1989: 'Mai the Psychic Girl' (with Kazuya Kudo) and 'Crying Freeman' (with Kazuo Koike).
This first series was one of the comics that started the success of manga in America, and the second was about the war of police and Japanese gangs against the Chinese mob. Other series that Ikegami made are 'Otoko Ozorga' (with Tetsu Kariya), 'Sanctuary', 'Strain' (with Sho Fumimura) and 'Nobunaga' (with Kazuya Kudo). Ikegami has additionally illustrated works like 'Katsuotoko Boï' (1991), 'Oritsuin Kumomaru no Shogaï' (1992), 'Kyoko' (1995-96), 'Odyssey' (from 1996), 'Heat' (from 1999) and 'Ruygetsu-sho' (from 2000).