Koji Kiriyama, also known by the name Kōji Kiriyama, is a Japanese manga artist recognized for creating the Ninku series. His original name in Japanese is written as 桐山光侍. He was born in the year 1968 and was raised in the Suginami ward of Tokyo, Japan. Kiriyama began his professional career in the manga industry with his debut in Weekly Young Magazine in 1989. His first major serialized work was Sengoku Koshien: Kyū inu-shi densetsu, a baseball-themed manga that was published in Shogakukan's Weekly Shonen Sunday magazine and later collected into six volumes between 1991 and 1992.

Kiriyama is best known as the original creator of the manga Ninku, which was serialized in Shueisha's influential Weekly Shōnen Jump magazine from June 1993 to September 1995. The series was compiled into nine tankōbon volumes. Ninku follows the story of a young boy named Fūsuke, a master of a fictional martial art that blends ninjutsu and kung fu, as he journeys with his pet penguin Hiroyuki. The series achieved significant commercial success, with over nine million copies in circulation. Following the conclusion of the original series, Kiriyama launched a sequel titled Ninku Second Stage: Stories of Etonins. This continuation ran in the seinen magazine Ultra Jump from September 2005 to September 2011 and was collected in twelve volumes.

The popularity of the Ninku manga led to its adaptation into multiple animated works. An original video animation (OVA) titled Ninku: Knife no Bohyō was produced and released in November 1994. This was followed by a fifty-five episode anime television series produced by Studio Pierrot, which aired on Fuji TV from January 1995 to February 1996. Additionally, an anime film simply titled Ninku: The Movie was released in July 1995. Kiriyama is credited as the original work author for all these anime productions.

Kiriyama's artistic identity is closely tied to action-oriented narratives that incorporate martial arts, ninja tropes, and a distinct sense of humor, exemplified by the unique character of a martial artist with a flatulent penguin companion. His work has been cited as an influence on later, highly successful manga artists. Notably, Masashi Kishimoto, the creator of Naruto, has stated that he used to copy Kiriyama's drawings while studying to become a manga artist. Furthermore, Hiroyuki Takei, known for creating Shaman King, worked as an assistant to Kiriyama during the 1990s. This places Kiriyama as a notable figure within the industry whose work contributed to the stylistic development of a subsequent generation of manga creators.