Li Jiancheng
in 626, Li Shimin, then locked in an intense rivalry with his older brother Li Jiancheng the Crown Prince and fearful that Li Jiancheng would kill him, set an ambush for Li Jiancheng and another brother, Li Yuanji the Prince of Qi, who supported Li Jiancheng, at Xuanwu Gate. Qin was one of the key commander of Li Shimin's forces, which subsequently killed Li Jiancheng and Li Yuanji. Li Shimin then effectively forced Emperor Gaozu to create him crown prince and then pass the throne to him (as Emperor Taizong).