Fabulous writer disordered as Poe (5)
I believe the answer is:
aesop
'fabulous writer' is the definition.
(writer of fables)
'disordered as poe' is the wordplay.
'disordered' indicates an anagram.
'as'+'poe'='aspoe'
'aspoe' is an anagram of 'AESOP'.
(Other definitions for aesop that I've seen before include "Greek storyteller" , "Fabulous man" , "Greek author of fables (c 620-560 BC)" , "classic author" , "Fable-teller" .)