First century BC Greek author of fables in which animals are given human characters and used to satirise human failings (5)
I believe the answer is:
aesop
(Other definitions for aesop that I've seen before include "story teller" , "Greek author, famous for his fables" , "Greek author of fables (c 620-560 BC)" , "he wrote in Greek" , "Poses as ancient Greek writer" .)