Kusunoki Masashige
Spying in Japan dates as far back as Prince Shōtoku (572–622). According to Shōninki, the first open usage of "ninjutsu" during a military campaign was in the Genpei War, when Minamoto no Kuro Yoshitsune chose warriors to serve as "shinobi" during a battle. This manuscript goes on to say that during the Kenmu era, Kusunoki Masashige frequently used "ninjutsu". According to footnotes in this manuscript, the Genpei War lasted from 1180 to 1185, and the Kenmu Restoration occurred between 1333 and 1336. "Ninjutsu" was developed by the samurai of the Nanboku-cho period, and further refined by groups of samurai mainly from Kōka and the Iga Province of Japan in later periods.