Ninja Gaiden is a media franchise based on 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 "side story" 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.

An action game is a video game genre that emphasizes physical challenges, including hand–eye coordination and reaction time. The genre includes a large variety of sub-genres, such as fighting games, beat 'em ups, shooter games, rhythm games and platform games. Multiplayer online battle arena and some real-time strategy games are also considered action games.