Diplomat and statesman. Born into the Nagano family of a goshi (country samurai), he was adopted by his grandfather, MATSUKI Muneyasu, a doctor and scholar of Western medicine, and studied Dutch studies, calling himself MATSUKI Koan. In 1856, he assisted as a professor at the Bansho Shirabesho (the Institute for Western Studies), and in 1861 he accompanied the Bunkyu Mission to Europe. In 1865 he went to Britain as a student of the Satsuma domain, studying abroad. After the Meiji Restoration, he served as a foreign judge and minister to Britain, and in 1873 he was appointed councillor and Minister of Foreign Affairs. He worked hard to improve the Ministry of Foreign Affairs at the time of its founding, including the conclusion of the Sakhalin Children Exchange Treaty and negotiations to restore tariff autonomy with the United States. He also served as president of the Senate, vice-president of the Privy Council, and more. He became an earl in 1884.