Tang Gaozu
Dou Dexuan himself was said to start his career in civil service when he was first an imperial university student during the reign of Emperor Yang of Sui. He served as a guard commander for Emperor Gaozu of Tang briefly before he seized the throne from Yang You, in 517 or 518. His activities during Emperor Gaozu's reign were not clear, but historical records indicated that he did not have much success in the political arena during Emperor Taizong's reign.