King Seon of Balhae (Dae Insu)

King Seon (personal name Insu, born Dae Insu) acceded to the throne in 818 as the tenth ruler of Balhae and was the first king to come from the line of Dae Ya-bal. He adopted the era name Geonheung and greatly expanded the kingdom's territory, organizing it into a system of five capitals, fifteen prefectures, and sixty-two districts. Under his reign Balhae reached its height and came to be known as the "Flourishing Land of the East" (Haedong Seongguk), making him the king who established the foundations of that golden age.