Koei Co., Ltd. was a Japanese video game publisher, developer, and distributor founded in 1978. The company is known for its Dynasty Warriors 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 the Dynasty Warriors and Samurai Warriors series, also known as the Musō series. Koei also owns a division known as Ruby Party, which focuses on otome 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.