Once upon a time, a ferocious tiger lived in a cave, and one day, feeling desperately hungry, it ventured out to hunt for food in the nearby wilderness.
In the wild, all sorts of animals roamed freely, but the moment they caught the distinct, pungent scent of a tiger, they would flee in an instant.
The tiger, seeing all this fine food just out of reach, felt a deep frustration it couldn't put into words. Just then, it spotted a man stumbling along a distant mountainside, so it lunged, killed him, and devoured every last bite of his flesh.
But the tiger was still unsatisfied. It seized the man's ghost and refused to let go, insisting he find another person for it to devour—otherwise, it would never set the ghost free.
The ghost captured by the tiger actually agreed to help. So it became the tiger's guide, searching until they finally encountered a second person.
At that moment, the ghost, desperate for its own release, actually began helping the tiger attack. It would first approach and bewilder any new person it encountered, then untie the victim's belt and remove their clothes, making it easier for the tiger to devour them.
This ghost that helps the tiger eat people is called a chang ghost. Based on this legend, later generations referred to helping evildoers commit heinous acts as "playing the jackal to the tiger."
Source: *Zhengzitong*, "Record of Listening to Rain"
Meaning of the Idiom: Later, the Chinese idiom "为虎作伥" came to describe helping evildoers commit heinous acts.