A thinker, educator, and journalist of the late Edo and Meiji periods. Born in Buzen Province (present-day Ōita Prefecture), he studied Dutch and English learning at Ogata Kōan's Tekijuku in Osaka. Through three visits to the United States and Europe in 1860, 1862, and 1867, he observed Western politics, economics, and culture, and on returning to Japan devoted himself to spreading modern thought through writing, education, and journalism. In 1868 he founded Keiō Gijuku (present-day Keio University). His representative work An Encouragement of Learning (Gakumon no Susume, 1872–76, a series) opens with the famous line "Heaven does not create one person above another, nor one person below another," criticizing the feudal social hierarchy and advocating individual independence, equality, and the importance of practical learning. The series became a bestseller of over 3.4 million copies. In An Outline of a Theory of Civilization (Bunmeiron no Gairyaku), he compared and analyzed Eastern and Western civilization. In his later years he published the newspaper Jiji Shimpō and remained active in journalism. He died at 66. His portrait appeared on the 10,000-yen note until 2024.