Li Yi
In 621, Emperor Gaozu's son Li Shimin the Prince of Qin (the eventual Emperor Taizong) captured Dou, and Emperor Gaozu executed Dou. For a short duration, Dou's domain submitted to Tang, but subsequently Dou's generals rose against Tang, led by Liu Heita. Emperor Gaozu sent a number of generals against Liu and ordered Li Yi to attack Liu from the north. Liu, however, was successful in defeating all Tang generals sent against him, including Li Yi, and regaining all of Dou's territory. Meanwhile, Youzhou was suffering from a famine. Gao agreed to supply Youzhou with food, and when Li Yi sent the weaker of his men to Wei Province to save them from the famine, Gao treated them well. Li Yi was pleased, and he sent three thousand men with several hundred wagons and over 1,000 horses and donkeys to Wei Prefecture to transport food. Gao, however, turned against Li Yi and kept all of them, breaking off the relations with Li Yi and Tang Dynasty. He allied himself with Eastern Tujue to the north and Liu to the south.