Koei Co., Ltd. is a Japanese video game publisher, developer, and distributor founded in 1978. The company is known for its historical simulation games based on the novel Romance of the Three Kingdoms, as well as simulation games based on pseudo-historical events.
The company has also found mainstream success in a series of loosely historical action games, the flagship titles of which are Dynasty Warriors (真・三國無双 (Shin Sangokumusō)) and Samurai Warriors (戦国無双 (Sengoku Musō)), the Musō (無双) series. Koei also owned a division known as Ruby Party, which focuses in dating sim games.
On April 1, 2009, Koei merged with Tecmo to form the Tecmo Koei Holdings holding company. Koei changed its name to Tecmo Koei Games on April 1, 2010 by absorbing Tecmo, and again on July 1, 2014 to Koei Tecmo Games. As of 2015, Koei Tecmo Games continues to use the Koei brand.