In the Western Han Dynasty, there was a cunning and ambitious man named Wang Mang, who, despite his outwardly virtuous acts, possessed a truly sinister and ruthless nature, embodying the idiom "鸱目虎吻" (owl's eyes and tiger's lips).

He meticulously cultivated a reputation for filial piety and integrity, for example, by diligently caring for his deceased brother's son and tirelessly attending to his ailing uncle. These calculated actions earned him widespread praise and allowed him to gain the trust of powerful figures, including Empress Dowager Xiaoyuan and the Emperor, who appointed him as a Palace Attendant.

Through extensive networking and political maneuvering, he steadily ascended the ranks, eventually becoming the Grand Sima and ultimately usurping the throne to establish his own dynasty.

However, once he held absolute power, his true "鸱目虎吻" disposition was fully unleashed. He became notoriously tyrannical, cruel, and ruthless, initiating widespread purges and killings to solidify his rule.

The idiom is used to describe a person with a fierce, sinister, and treacherous appearance or character, much like Wang Mang's true self.