Wei Zheng
Wei Zheng was born to a poor family in modern Hebei, and joined Li Mi's rebellion against the Sui dynasty in his youth. After Li Mi's submission to the Tang Empire, Wei Zheng became a Tang official and eventually served on the staff of Li Jiancheng, the Crown Prince and eldest son of Emperor Gaozu, the Tang dynasty's founding emperor. As such, he served against the interests of Li Jiancheng's younger brother, Li Shimin (the Prince of Qin), with whom Li Jiancheng was locked in an intense rivalry. In 626, Li Shimin ambushed and killed Li Jiancheng, and then effectively forced Emperor Gaozu to yield the throne to him. Rather than punishing Wei Zheng, however, he was impressed with Wei's faithfulness to Li Jiancheng, and he made Wei an important official, eventually a chancellor. Wei Zheng's promotion to this position gave him far broader freedom to criticise others, particularly the emperor, than other officers of the court. He emphasized propriety and opposed overextending the state. His advice and criticism were not always accepted, but in accordance with Confucian etiquette, the emperor would concede to his suggestions with some regularity.