Prince of Qin
During the reign of Sui's successor dynasty Tang Dynasty's founder Emperor Gaozu, Du Zhenglun was initially serving as the military advisor to the commandant at Qi Prefecture (齊州, roughly modern Jinan, Shandong). Emperor Gaozu's son, the major general Li Shimin the Prince of Qin became aware of Du's talents, and invited him to serve as a resident scholar at Li Shimin's mansion.