Mugaku Sogen, also known as Bukko Kokushi (September 3, 1226 – September 22, 1286) is a prominent Zen Buddhist monk of the thirteenth century in Japan, an emigre from Song Dynasty China.

He is adviser to Japan's most powerful ruler of the day, the regent of the Shogun (Shikken) Hōjō Tokimune (as opposed to an Imperial Regent).

He founds the Zen temple Engaku-ji in Kamakura, one of Japan's five most important Zen temples.