Saitō Hajime (斎藤 一) (born Yamaguchi Hajime (山口 一); February 18, 1844 – September 28, 1915) was a Japanese samurai of the late Edo period, who most famously served as the captain of the third unit of the Shinsengumi. He was one of the few core members who survived the numerous wars of the Bakumatsu period. He was later known as Fujita Gorō (藤田 五郎) and worked as a police officer in Tokyo during the Meiji Restoration.
