李承乾
On 25 June 635, Emperor Gaozu died. Emperor Taizong observed a period of mourning for him. During that time, Li Chengqian formally ruled on important matters of state for about 45 days, after which Emperor Taizong resumed his imperial authority, but still had Li Chengqian rule on more minor issues. It was around this time that Li Chengqian was said to have good judgment and logical abilities. From this point on, whenever Emperor Taizong was away from the capital Chang'an, Li Chengqian would be in charge of the imperial government.