Today, we use the phrase to mean someone is complaining when nothing's really wrong. It's also used when a person asks for help when he doesn't need it. For example: "The governor says if our taxes aren't doubled, he'll have to close all of our schools. But he's just crying wolf."
So, who is this wolf we speak of? It comes from an Aesop fable. Aesop was a former Greek slave in the late to mid-sixth century B.C.E. when he allegedly penned (or related) hundreds of morality tales, collectively known as known as "Aesop's Fables" [source: Horgan].
One was about a young shepherd boy who was bored while tending the sheep all day. So to drum up a little excitement and have some company, he ran toward the village screaming, "Wolf! Wolf!" The villagers ran out to meet him, and some stayed a while. Score! The boy was so happy that he repeated his trick a few days later. Once again, the villagers ran out to him, only to find, once again, that there was no wolf. Then, disaster struck — a real wolf trotted out of the forest and threatened the boy's flock. He cried, "Wolf! Wolf!" a third time, but no one ran out. The villagers were tired of his tricks. The moral, says Aesop, is that "A liar will not be believed, even when he speaks the truth."