Ōmura Masujirō was a Japanese military leader and theorist in Bakumatsu period Japan. He was the "Father" of the Imperial Japanese Army, launching a modern military force closely patterned after the French system of the day.

Bakumatsu was the final years of the Edo period when the Tokugawa shogunate ended. Between 1853 and 1867, under foreign diplomatic and military pressure, Japan ended its isolationist foreign policy known as sakoku and changed from a feudal Tokugawa shogunate to the modern empire of the Meiji government. The major ideological-political divide during this period was between the pro-imperial nationalists called ishin shishi and the shogunate forces, which included the elite shinsengumi swordsmen.