Founded by couple Kou Shibusawa and Keiko Erikawa in 1978, Koei established several genres in the Japanese gaming industry. They laid the foundations for Japanese RPGs with games like The Dragon & Princess in 1982 and the eroge genre with games like Night Life in 1982. They then became best known for historical strategy games, after the influential strategy title Nobunaga's Ambition in 1983. While they primarily worked on Japanese computer games, they would eventually start producing games for consoles as well, adapting many of their strategy games for the limited console interface.
Today they are best known for the Romance of the Three Kingdoms and Dynasty Warriors/Musou franchises as well as their many other strategy and simulation games, most of which are set in the Three Kingdoms period of Ancient China or the Sengoku era of Medieval Japan.
In 2009 Koei merged with Tecmo to become Tecmo Koei (which was later renamed Koei Tecmo). At this point, Koei Co. Ltd. was effectively defunct.