Hou Sizhi (侯思止) (died 693) was a secret police official during the Chinese dynasty Tang Dynasty and Wu Zetian's Zhou Dynasty. It is not known when Hou Sizhi was born, but it is known that he was from Tang's capital prefecture Yong Prefecture (雍州, roughly modern Xi'an, Shaanxi). He was said to be poor and unable to make a living from selling bread, and so he served as a servant at the household of the general Gao Yuanli () in Heng Prefecture (恆州, roughly modern Shijiazhuang, Hebei). In 690, he was accused of inappropriate conduct, and the prefect of Heng Prefecture, Pei Zhen, was set to sentence him to caning. A local official advised him to make a secret report to Wu Zetian, who was then empress dowager and regent over her son Emperor Ruizong, and he did so, accusing Pei and Emperor Ruizong's granduncle Li Yuanming () the Prince of Shu of plotting treason together. Empress Dowager Wu, already looking for excuses to act against senior members of the Li imperial clan, exiled Li Yuanming and executed Pei and Li Yuanming's son Li Dan () the Prince of Yuzhang. She gave Hou a general title, but Hou offered to become an assistant censor, which was ranked lower but which had the authority to investigate crimes. Empress Dowager Wu asked him, "You are illiterate. How can you be a censor?" Hou responded, "A xiezhi is also illiterate, but it could use its horn to hit the evil!" (The xiezhi was a mythical one-horned animal that was intelligent, and whenever it saw two people fighting, it would use its horn to hit the wrong side.) Empress Dowager was pleased and made him a censor. On one occasion, she was set to award a house to Hou that was seized from a person accused of treason. Hou declined and stated, "I hate treasonous individuals, and I do not want a house from one!" She was further impressed. In 692 (by which time Wu Zetian had seized the throne from Emperor Ruizong and established her own Zhou Dynasty), a number of officials—the chancellors Ren Zhigu, Di Renjie, and Pei Xingben, along with other officials Pei Xuanli (), Lu Xian (), Wei Yuanzhong, and Li Sizhen () -- were accused of treason. The secret police official Lai Junchen was in charge of the investigations, but Hou was specifically charged with interrogating Wei. Wei refused