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