Emperor Gaozu of Tang

Li Yuan was governor of the Shanxi region under the Sui dynasty, garrisoning the north and learning to manage the Göktürks. When the Sui fell apart in July 617, his second son Li Shimin urged him into open rebellion. Li Yuan declared himself "Great Chancellor," propped up a child puppet emperor named Yang You, then swept him aside in 618 to establish the Tang with himself as Emperor Gaozu. He and Li Shimin - now Prince of Qin - spent the next decade crushing rival warlords one by one until China was unified under Tang rule by 628. Gaozu lowered taxes, redistributed land, scrapped the Sui's brutal legal code, and laid the groundwork for what would become the dynasty's golden age. In 626 Li Shimin ambushed and killed his two brothers at Xuanwu Gate in a succession struggle; Gaozu, afraid of his own son, abdicated and lived out his last nine years as retired emperor.