Aesop, or Æsop (from the Greek Αἴσωπος Aisopos), is known for his fables. He was, by tradition, a slave of African descent who lived from about 620 BC to 560 BC in Ancient Greece. 

Aesop's Fables are still taught as moral lessons and used as subjects for  entertainment, especially children's plays and cartoons. Aesop is said to have written thousands of fables, but none has been verified. This means we do not know whether he wrote any, or perhaps just collected them. His most famous one was perhaps The Lion and the Mouse.

No writings by him survive. Tales credited to him were gathered across the centuries and in many languages. This is a storytelling tradition that continues to the present day. Many of the tales have animals and inanimate objects that speak, solve problems, and generally have human characteristics.

The tradition is that he was at one point freed from slavery and that he eventually died at the hands of Delphians. In fact, the doubt about his life has led some to deny his existence altogether.

His most famous fable is a parable of the tortoise and the hare. In this story, a rabbit challenges a tortoise to a race. The rabbit is sure of its victory and as a result, depending on the version of the story, in some way completes the race slower than the turtle. Often, the hare takes a nap or takes too many breaks. The persistent tortoise, despite being slower, wins because it persevered.

Aesop's Fables 

Aesop's Fables or Aesopica refers to a collection of fables credited to Aesop. Aesop's Fables has also become a blanket term for collections of brief fables, usually involving personified animals.

The fables remain a popular choice for moral education of children today. Many stories included in Aesop's Fables, such as The Fox and the Grapes (from which the idiom "sour grapes" was derived), The Tortoise and the Hare (see Zeno's paradoxes) and The Shepherd Boy and the Wolf (also known as The Boy Who Cried Wolf), are well-known throughout the world.

Sources 

Caxton, John, 1484. The history and fables of Aesop, Westminster.  Modern reprint edited by Robert T. Lenaghan (Harvard University Press: Cambridge, 1967).
Caxton's famous Epilogue
Bentley, Richard, 1697. Dissertation  upon the Epistles of Phalaris...  and the Fables of Æsop. London.
Jacobs, Joseph, 1889. The Fables of Aesop: Selected, Told Anew, and Their History Traced, as first printed by William Caxton, 1484, from his French translation
i. A short history of the Aesopic fable
ii.  The Fables of Aesop
Handford, S. A., 1954. Fables of Aesop. New York: Penguin.
Perry, Ben E. (editor), 1965. Babrius and Phaedrus, (Loeb Classical Library) Cambridge: Harvard University Press, 1965. English translations of 143 Greek verse fables by Babrius, 126 Latin verse fables by Phaedrus, 328 Greek fables not extant in Babrius, and 128 Latin fables not extant in Phaedrus (including some medieval materials) for a total of 725 fables.
Temple, Olivia and Robert (translators), 1998. Aesop, The Complete Fables,  New York: Penguin Classics. ()
Bryn Mawr Classical Review, with Aesop bibliography

Other websites 

Aesop's Fables
 Aesopica.net – Over 600 English fables, with Latin and Greek texts also – Searchable
 AesopFables.com – Large collection of fables, but many fables are NOT Aesopic
 Free audiobook of Aesop's Fables  from LibriVox
 The Fables – A site primarily for children 

620 BC births
560 BC deaths
Ancient Greek writers
Slaves