Ninja Gaiden is a series of action video games by Tecmo featuring the ninja Ryu Hayabusa as its protagonist. The series was originally known as Ninja Ryukenden in Japan. The word "gaiden" in the North American Ninja Gaiden title means “tale” in Japanese. The original arcade version, first two Nintendo Entertainment System games and Game Boy game were released as Shadow Warriors in PAL regions. As of 2008, the series has shipped over 7.7 million copies.