Some important texts were created and studied by scholars. Philosophical works written by Yang Xiong (53 BC – 18 AD), Huan Tan (43 BC – 28 AD), Wang Chong (27–100 AD), and Wang Fu (78–163 AD) questioned whether human nature was innately good or evil and posed challenges to Dong's universal order. The Records of the Grand Historian by Sima Tan (d. 110 BC) and his son Sima Qian (145–86 BC) established the standard model for all of imperial China's Standard Histories, such as the Book of Han written by Ban Biao (3–54 AD), his son Ban Gu (32–92 AD), and his daughter Ban Zhao (45–116 AD). There were dictionaries such as the Shuowen Jiezi by Xu Shen (c. 58 – c. 147 AD) and the Fangyan by Yang Xiong. Biographies on important figures were written by various gentrymen. Han dynasty poetry was dominated by the fu genre, which achieved its greatest prominence during the reign of Emperor Wu.