李建成
In 626, Li Shimin, then locked in an intense rivalry with Li Jiancheng (who, as the older brother, was crown prince), feared that Li Jiancheng was about to kill him, and ambushed Li Jiancheng and Li Yuanji (who supported Li Jiancheng) at Xuanwu Gate and killed them. He then effectively forced Emperor Gaozu to create him crown prince and then yield the throne to him (as Emperor Taizong). Although Pei Ji appeared to have supported Li Jiancheng in the struggle, Emperor Taizong initially continued to honor him, and on one occasion, when Emperor Taizong was offering sacrifices to heaven outside the capital, he requested Pei and Zhangsun Wuji to ride with him in the imperial wagon, a great honor at the time.