Jang Bo-go (Choi Soo Jong) was a slave from Shilla (a Korean dynasty that lasted from 57 B.C. until 935 A.D.) He was sold in China during the Tang Dynasty, where he was trained as a gladiator-slave. Through hardwork and perseverance, he made it back to Shilla and became a successful sea merchant. The sea passage at the time was plagued by pirates and Jang Bo-go went head to head with them in battles and managed to keep the pirates at bay. This epic drama tells the story of a historical figure blending it with intrigue and battle of wit to make it into a successful drama of all times.

Source: Touya (http://kdrama.com/forum/index.php?showtopic=61)