Li Jiancheng
Dai Zhou's activities for the next few years were not clear. In 626, Li Shimin, locked in an intense rivalry with his older brother Li Jiancheng the Crown Prince and fearing that Li Jiancheng would kill him, ambushed Li Jiancheng and another brother who supported Li Jiancheng, Li Yuanji the Prince of Qi, at Xuanwu Gate and killed them. He then effectively forced Emperor Gaozu to first create him crown prince and then yield the throne to him (as Emperor Taizong). Once he took the throne, he made Dai an assistant to the minister of defense, and he also created Dai the Baron of Wuchang.