Emperor Han Chengdi 漢成帝 (r. 33-7 BCE), personal name Liu Ao 劉驁, courtesy name Jun 俊, was a ruler of the Former Han dynasty 前漢 (206 BCE-8 CE). He was a son of Emperor Yuan 漢元帝 (r. 49-33 BCE) and Empress Wang 王皇后 (Wang Zhengjun 王政君) and succeeded his father to the throne.
When he succeeded to the throne, he made his brother-in-law Wang Feng 王鳳 General-in-chief serving as commander-in-chief (da sima da jiangjun 大司馬大將軍) and entrusted him the duties of the Imperial Secretariat (shangshu 尚書). From that point on the family Wang became stronger and stronger and would eventually, under Wang Mang 王莽, end the Former Han dynasty. Five uncles were all bestowed titles of nobility: Wang Tan 王譚 was given the title of Marquis of Ping'a 平阿侯, Wang Shang 王商 as Marquis of Chengdu 成都侯, Wang Li 王立 as Marquis of Hongyang 紅陽侯, Wang Gen 王根 as Marquis of Quyang 曲陽侯, and Wang Feng 王逢 as Marquis of Gaoping 高平侯.
Wang Feng took over the business of administering the empire, while Emperor Cheng refused to engage in any obligations. He highly esteemed the scholar Liu Xin 劉歆 for his poetry and wanted to appoint him Palace attendant-in-ordinary (zhongchangshi 中常侍), but Wang Feng did not allow this promotion.
Because Emperor Cheng had no children, he made his brother Liu Kang 劉康, Prince Gong of Dinggao 定陶共王康, make resident regent staying in the capital to take care of things (liushou 留守), and again, Wang Feng contradicted this step and sent Prince Gong home to Dingtao.
Instead of ruling, Emperor Cheng loved cockfights, riding and traveling, and lived like a commoner. In 22 BCE he stayed during one of his travels at the court of Princess Yang'a 陽阿公主, who entertained him with a banquet during which the dancer Zhao Feiyan 趙飛燕 and her sister performed their arts. The emperor was so enchanted by the girls that he introduced them into his "harem". Empress Xu 許皇后 and Lady Ban 班倢伃, who belonged to the same family like the later historian Ban Gu 班固, lost his favour, and Zhao Feiyan was made empress.
The ministers remonstrated against the growing power of the family Zhao (Feiyan's father Zhao Lin 趙臨 was ennobled as Marquis of Chengyang 成陽侯), but the emperor refused their criticisms.
In 8 BCE, he appointed his nephew Liu Xin 劉欣, the Prince of Dingtao, heir apparent. Emperor Cheng was buried in the tomb mound Yanling 延陵 and was succeeded by Liu Xin, who is known as Emperor Ai 漢哀帝 (r. 7-1 BCE).