Li Yuanji
In 626, Li Shimin, in a dispute with his brothers Li Jiancheng, the Crown Prince, and Li Yuanji, the Prince of Qi, ambushed Li Jiancheng and Li Yuanji at Xuanwu Gate, killing them. Fearful of what Li Shimin might do next, Emperor Gaozu passed the throne to him and became "Taishang Huang" (retired emperor). He died on 25 June 635.