Who they were
He served in office repeatedly but kept withdrawing to study in his native Andong region. His mature thought was developed partly in the famous “Four–Seven debate”, a correspondence on the moral emotions.
What they did
His philosophy gave principle (i, or li) an active role in moral life. For the young king he distilled his teaching into the “Ten Diagrams on Sage Learning” (1568). His study hall grew into the Dosan Seowon academy, among the Korean seowon inscribed by UNESCO in 2019.
Legacy
His school shaped Korean Confucianism for centuries, and his works were studied intensively in Tokugawa Japan. His portrait appears on South Korea’s 1,000-won note, and he remains the deepest philosophical voice of the Joseon tradition.