Li Jiancheng (李建成) (589 – July 2, 626), formally Crown Prince Yin (隱太子, literally, "the hidden crown prince"), nickname Pishamen (毗沙門), was a crown prince of the Chinese dynasty Tang Dynasty. He was the oldest son of the founding emperor Emperor Gaozu (Li Yuan) and therefore was designated crown prince after the founding of the dynasty in 618. However, although he himself was fairly capable as a general, he was overshadowed by the contributions of his younger brother Li Shimin the Prince of Qin, and the brothers contended for power for years, with Li Jiancheng aided by another younger brother, Li Yuanji the Prince of Qi. In 626, Li Shimin, fearing that Li Jiancheng and Li Yuanji were about to kill him, laid an ambush for them at Xuanwu Gate outside the palace and killed them. Li Shimin then effectively forced Emperor Gaozu to yield the throne to him (as Emperor Taizong).
Read more about Li Jiancheng: Background, Participation in Tang's Founding, Rivalry With Li Shimin, Death