Chang Po-go (died 846) was a Korean adventurer and merchant prince whose name was once synonymous with Korean maritime dominance in eastern Asia in the early 9th century.
Son of a fisherman from Wan Island off the southwestern coast of the Korean peninsula, Chang Po-go early migrated to T'ang China, where he rose to be a captain in Hsü-chou in the lower Huai River valley. Returning to Korea in 828, he alerted the throne over the danger of Chinese piracy in the Yellow Sea, whereupon the King appointed him commissioner of Ch'onghaejin, the military headquarters of Wan Island. Chang raised a private navy, which at times numbered 10,000 men, by which he controlled the ocean commerce between China, Korea, and Japan.
The ships engaged in this international trade were owned and manned by Chang, and Korean trading communities flourished along the southern coast of the Shantung Peninsula and the lower reaches of the Huai. Some of these colonies enjoyed extraterritorial privileges, such as the famous Mount Ch'ih community, which over looked the sea route between China and Korea. These communities often served as an intermediary between Chinese authorities and Japanese visitors, as in the case of the Japanese pilgrim Ennin, who at one time addressed a letter to Chang for his assistance and shelter.
In 837 Chang was involved in a royal succession struggle. From the end of the 8th century on, the Silla court was beset by contention between the rising aristocracy and the authoritarian monarchy based on the bone rank (bloodline) system. Hence the throne, hitherto determined solely by bloodline, came to require political skill and military might. Often a contender, to bolster his claim, had to ally himself with local chiefs who were disillusioned nobles, depending for their power on private soldiers recruited from serfs and vagrants. In 839 the son of the former king's rival Kyunjong, with military assistance from Chang, succeeded in overthrowing his rival and ascending the throne as Sinmu.
History relates that the downfall of Chang was connected with his efforts to marry off his daughter to the King. The marriage alliance had probably been promised by Sinmu during his protracted sojourn on Wan Island, but because of his untimely death Chang sought to force Sinmu's successor-son to abide by the promise. Chang's attempt in 845 to force the throne to adopt his daughter as royal consort irritated the central aristocracy, who frowned upon such an alliance as unsavory and potentially dangerous. Chang's death by assassination is traditionally placed in 846, but it may have occurred a few years earlier. In 851 Ch'onghaejin was abolished as a military base, and thus ended the maritime kingdom of Chang Po-go, and with it the brief Silla maritime dominance in eastern Asia.
There is no full-length biography of Chang in English. He is discussed in Edwin O. Reischauer, Ennin's Travels in T'ang China (1955).