Tian Chengsi
Tian Chengsi was born in 705, during the reign of Emperor Zhongzong of Tang. His family was from Ping Prefecture (平州, roughly modern Qinhuangdao, Hebei), and his ancestors, for several generations, had served in the military. His grandfather Tian Jing () and father Tian Shouyi () both had reputations for upholding justice in the region. Late in the reign of Emperor Zhongzong's nephew Emperor Xuanzong, Tian Chengsi served as a forward commanding officer under the general An Lushan, the military governor ("jiedushi") of Fanyang Circuit (范陽, headquartered in modern Beijing), and particularly impressed An with his ability to maintain strict military discipline. For his contributions in campaigns against the Khitan and the Xi tribes, he was promoted several times, eventually to be a general under An.