The English idiom “cry wolf” means to sound a false alarm or to ask for assistance when no assistance is there. To say that someone cried wolf also carries the implication that no one will respond to the person’s pleas for help should the person should ever really need assistance because of the false reporting in the past.
The origins of the phrase cry wolf are in one of Aesop’s Fables, titled The Boy Who Cried Wolf or The Shepherd Boy and the Wolf. The fables, collected by Aesop in 5th-century Greece, told stories that taught moral lessons by showing the outcomes of their characters' bad behavior. At the end of his fables, Aesop told exactly what the moral meaning of his tale was. The moral is explained as meaning that liars aren’t believed even when they tell the truth.
In the story, a boy is sent to guard sheep but becomes bored. He entertains himself by crying out for help, saying a wolf is among the sheep. The people of the village respond each time the boy cries wolf, only to realize the boy is again making up the report of danger and laughing at them for responding to his false cries of danger.
Eventually a wolf really does get among the sheep, and the boy does cry wolf. By this point, however, the villagers ignore the boy’s cries for help, believing he is again making up the story out of boredom. The boy and the sheep are attacked by the wolf and killed, because no one responds to help the boy because of his false reporting in the past.
It was not until 1692 that the fable was first told in English in Roger L’Estrange’s translation. As the fable’s popularity grew and more and more people learned the story of the little boy who cried wolf, most would have come to understand the phrase as a warning not to sound false alarms or would understand that to cry wolf meant someone had given a false report. The idiom likely entered into popular language in the 19th century.
Both the fable and the phrase are still used in contemporary culture. The fable is read and told to children to teach them about the consequences of telling untruths. The phrase has also lent itself to titles and references in literature and music.