Aesop's Fables is a collection of children's stories that attempt to convey a moral. According to Herodotus, the fables were invented by a Greek slave named Aesop in the 6th Century B.C, though other ancient writers offer many different nationalities and time periods for Aesop: it may well be that Aesop did not exist, and that the fables attributed to him are merely folktales of unknown origins.
Though there are hundreds of fables ascribed to Aesop, a few have become truly famous. The Tortoise and the Hare is the story of the race between a rabbit and a tortoise, which is lost by the much-faster rabbit due to his laziness. The story, like many of those atributed to Aesop, ends with a moral. In this case, the moral is usually stated as "slow and steady wins the race".
Another of Aesop's more famous fables is The Fox and the Grapes, in which a fox wishes to eat a bunch of grapes but cannot because they are too high for him to reach. The fox concludes (rationalizing the situation to himself) that, because he cannot reach them, the grapes must be sour. From this fable, the expression "sour grapes" has entered the English language.