Aesop may not have written his fables. The Aesop Romance claims that he wrote them down and deposited them in the library of Croesus; Herodotus calls Aesop a "writer of fables" and Aristophanes speaks of "reading" Aesop, but no writings by Aesop have survived. Scholars speculate that "there probably existed in the fifth century [BCE] a written book containing various fables of Aesop, set in a biographical framework." Sophocles in a poem addressed to Euripides made reference to Aesop's fable of the North Wind and the Sun. Socrates while in prison turned some of the fables into verse, of which Diogenes Laertius records a small fragment. The early Roman playwright and poet Ennius also rendered at least one of Aesop's fables in Latin verse, of which the last two lines still exist.  The body of work identified as Aesop's Fables was transmitted by a series of authors writing in both Greek and Latin. Demetrius of Phalerum made a collection in ten books, probably in prose (Aisopeion a) for the use of orators, which has been lost. Next appeared an edition in elegiac verse, cited by the Suda, but the author's name is unknown. Phaedrus, a freedman of Augustus, rendered the fables into Latin in the 1st century CE. At about the same time Babrius turned the fables into Greek choliambics. A 3rd-century author, Titianus, is said to have rendered the fables into prose in a work now lost. Avianus (of uncertain date, perhaps the 4th century) translated 42 of the fables into Latin elegiacs. The 4th-century grammarian Dositheus Magister also made a collection of Aesop's Fables, now lost.  Aesop's Fables continued to be revised and translated through the ensuing centuries, with the addition of material from other cultures, so that the body of fables known today bears little relation to those Aesop originally told. With a surge in scholarly interest beginning toward the end of the 20th century, some attempt has been made to determine the nature and content of the very earliest fables which may be most closely linked to the historic Aesop.

Answer this question "What did Aesop do as a fabulist?" by extracting the answer from the text above.
The Aesop Romance claims that he wrote them down and deposited them in the library of Croesus;