Empress Zhangsun
Li Chengqian was created crown prince in 626 at the age of eight (by East Asian reckoning), after his father became emperor on 4 September. In his youth, he had a reputation for good judgment, but was also said to be suffering from a foot illness. Later on, he was said to be frivolous, favoring Tujue customs instead of studying about ways to rule an empire. He lost favor in Emperor Taizong's eyes to a younger brother, Li Tai the Prince of Wei. (Both had the same mother, Emperor Taizong's wife Empress Zhangsun.) In 643, in fear that Emperor Taizong was about to depose him in favor of Li Tai, he plotted with the general Hou Junji to overthrow Emperor Taizong. The plot was discovered, and he was deposed and reduced to commoner rank, but Emperor Taizong, believing that Li Tai to be responsible for Li Chengqian's downfall, appointed yet another son, Li Zhi (also by Empress Zhangsun), crown prince instead. Li Chengqian was exiled, and died in exile in January 645, as a commoner under house arrest. He was posthumously granted an imperial prince title during the reign of his grandnephew, Emperor Xuanzong after his grandson Li Shizhi became chancellor.