Oji Hiroi, born Teruhisa Hiroi on February 8, 1954, in Tokyo, is a Japanese multi-creator known for his foundational work across the anime, manga, and video game industries. He is the founder of Red Entertainment and has held positions such as an advisor to several companies and a visiting professor at Kanazawa Institute of Technology.

Hiroi began his career in the entertainment industry after leaving Rikkyo University. He founded the company that would become Red Entertainment and initially worked on planning character merchandise and toys. His first major success as an anime original creator came with the Sunrise production Mashin Hero Wataru (1988). He is the original creator of many anime series from the late 1980s and 1990s, including Madō King Granzort (1989), its subsequent sequels and OVAs such as Madō King Granzort: The Final Magical Battle (1990), Madō King Granzort: Bōken-hen (1992), and Madō King Granzort: Non-Stop Rabi. Additional anime credits from this period include RPG Densetsu Hepoi, Genji Tsūshin Agedama, and Kūsō Kagaku Sekai Gulliver Boy. He later created the anime series Kita e. Diamond Dust Drops, also known as Diamond Daydreams.

Beyond his direct work in television animation, Hiroi is internationally recognized for creating major video game franchises, most notably Sakura Wars (Sakura Taisen) and Far East of Eden (Tengai Makyō). He served as the original creator and general producer for the Sakura Wars series, which expanded from video games into a large media franchise including numerous anime adaptations, OVAs, and a theatrical film. He also wrote the Sakura Wars manga. His other original anime creations that originated from his game work include the OVA series Virgin Fleet and Kidō Shinsengumi Moeyo Ken.

Hiroi has also worked as a stage director, drawing on his early exposure to theater. The Takarazuka Revue, an all-female musical theater troupe, directly inspired the concept of the Sakura Wars series, which combines strategic combat with a life simulation set in a theater company. He has occasionally performed minor voice acting roles in adaptations of his own works, such as appearing as an audience member in the Sakura Wars OVA Su・mi・re.

In the industry, Hiroi is regarded as a significant figure for bridging the gap between anime and video game production in the 1990s. He has shared his perspective on the differences between the Japanese and American entertainment industries, noting his experience working with studios like Lucasfilm and Pixar. Reflecting on Japan's game industry, he has criticized the trend of producing lower-cost sequels to successful titles, arguing that this approach hindered long-term growth and global competitiveness, particularly when the domestic market was thriving. His contributions to the content industry have been recognized by the Content Industry History Archive Research Center (HARC), which has conducted oral history interviews with him to preserve his legacy.