Fabulous writer dishevelled as Poe (5)
I believe the answer is:
Here is my best explanation:
'fabulous writer' is the definition.
(writer of fables)
'dishevelled as poe' is the wordplay.
'dishevelled' indicates anagramming the letters.
'aspoe' is an anagram of 'AESOP'.
(Other definitions for aesop that I've seen before include "A pose by Greek writer of fables", "He wrote", "Author of many fables", "Greek storyteller", "Storyteller", "Fabulous writer", "Greek fable writer", "Greek author, famous for his fables", "Writer of fables" and "Fable writer".)