Koei Co., Ltd. was 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 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. Koei was established in July 1978 by Yōichi Erikawa (also known as Kou Shibusawa) and Keiko Erikawa. Yoichi was a student at Keio University, and when his family's rural dyestuffs business failed, he decided to pursue his interest in programming. The company has remained located in the Hiyoshi area of Yokohama. The company initially focused on personal computer sales and made-to-order business software. In 1982, the company released the erotic title (eroge) Seduction of the Condominium Wife, which was an early role-playing adventure game with color graphics, owing to the eight-color palette of the PC-8001 computer. It became a hit, helping Koei become a major software company. In March the same year Koei released Underground Exploration, the earliest known Japanese RPG. In 1983 it released Nobunaga's Ambition, a historical strategy game set during the Sengoku period of Japanese history. The game went on to receive numerous awards, and Koei produced several more such games set against the backdrop of world history, including Romance of the Three Kingdoms, set during the Three Kingdoms period of Chinese history, and Uncharted Waters, set in Portugal during the Age of Exploration. In 1988, Koei established a North American subsidiary, Koei America Corporation, in California.