Who they were
Born to humble origins on an island, he first made his career as a military officer in Tang China. Returning to Silla, he persuaded the court to let him found the Cheonghaejin garrison on Wando island in 828, to suppress the pirates and the slave trade preying on Koreans.
What they did
From Cheonghaejin his fleets came to dominate the triangular trade among Silla, Tang and Japan. The travel diary of the Japanese monk Ennin documents the reach of his network, including his monastery on the Shandong coast. Drawn into Silla’s royal succession politics, he was assassinated by an agent sent by the court — in 841 according to Japanese sources, or 846 according to the Samguk Sagi. Cheonghaejin was dissolved soon after.
Legacy
He is celebrated as Korea’s pioneer of maritime trade, and a modern South Korean navy submarine class bears his name.