Li Chengqian
In 643, with Li Chengqian, then crown prince, and Li Tai, locked in an intense rivalry, Li Chengqian plotted to overthrow Emperor Taizong and was deposed. Emperor Taizong initially wanted to make Li Tai crown prince, but soon, believing that Li Tai's machinations were responsible for Li Chengqian's downfall, exiled Li Tai as well and created their younger brother, his ninth son Li Zhi the Prince of Jin, the new crown prince, believing Li Zhi to be kind. (Li Chengqian, Li Tai, and Li Zhi were all born of Emperor Taizong's wife Empress Zhangsun.) Later, however, he began to believe that Li Zhi's personality was too weak and worried that he would not be appropriate as an emperor, he showed this his worry once, said he may considered making Li Ke crown prince instead. Li Zhi's uncle Zhangsun Wuji opposed this immediately, and Emperor Taizong did not do so, but an enmity thereafter developed between Zhangsun Wuji and Li Ke.