Mugaku Sogen (無学祖元), also known as Bukko Kokushi (September 3, 1226 – September 22, 1286) was a prominent Zen Buddhist monk of the 13th century in Japan, an emigre from Song Dynasty China. He was 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 founded the Zen temple Engaku-ji in Kamakura, one of Japan's five most important Zen temples.