During the Spring and Autumn period, Duke Huan of Qi was the hegemon among the feudal lords, and his prime minister Guan Zhong was renowned for his wisdom. Together, they made Qi a formidable power.
One day, Duke Huan of Qi was chatting with Guan Zhong and asked, "What do you think is the greatest concern for the state?" Guan Zhong thought for a moment and replied, "The temple rats and fierce dogs." Duke Huan, puzzled, asked, "What are temple rats and fierce dogs?"
Guan Zhong explained to Duke Huan of Qi, "The shrine's deity statue is made of wood and clay, and rats live inside it, called 'shrine rats.' These rats gnaw on the statue and destroy the shrine's contents, yet you cannot eliminate them. In the shrine, you can neither burn them out nor flood them out, because fire or water would damage the shrine itself."
"As for the fierce dog, it is said that long ago there was a brewer who made fine wine to sell. Yet year after year, he sold none at all. Why? Because he kept a vicious wolfhound that would lunge and bite anyone who entered the courtyard, scaring all the customers away."
Guan Zhong concluded, "Your Majesty, for a nation, the treacherous ministers beside the ruler are the temple rats; the petty men in power are the fierce dogs. Thus, what a state most fears are temple rats and fierce dogs."
Duke Huan of Qi nodded and said, "Ah! I understand." Later, the idiom "Rat in the Altar, Fierce Dog" came to be used as a metaphor for wicked and evil people.
Source: *Han Feizi*, "Shuo Lin Shang"
Meaning of the Idiom: Later, the Chinese idiom "社鼠猛狗" came to describe a metaphor for wicked and evil people.