窦建德
At that time, the Eastern Turkic Khaganate's Shibi Khagan was married to Princess Yicheng, previously his stepmother and a member of the Yang family. At Princess Yicheng's request, Dou Jiande — who was eager to enter into an alliance with the Turks — delivered remnants of the Yang family, including the former Empress Xiao and Yang Zhengdao, to the north of the Great Wall where they were welcomed into Turkic territory. The Turks realized the usefulness of a puppet government which could rally Sui loyalists to their side; so in 620, Shibi's successor Chuluo Khagan established Yang Zhengdao as the King of Sui, including a "Branch Department of State Affairs", in Dingxiang Commandery.