Wang Shizhen
Wang Chengyuan was born in 801, during the reign of Emperor Dezong. He was a son of Wang Shizhen, who, around the time, took over as military governor ("Jiedushi") of Chengde after the death of Wang Chengyuan's grandfather Wang Wujun. He had two elder brothers Wang Chengzong, Wang Chengxi () and at least three younger brothers — Wang Chengtong (), Wang Chengdi (), and Wang Chengrong ().