... as Poe could be a fabulous writer (5)
I believe the answer is:
aesop
'a fabulous writer' is the definition.
(writer of fables)
'as poe could be' is the wordplay.
'could be' indicates an anagram.
'as'+'poe'='aspoe'
'aspoe' anagrammed gives 'AESOP'.
(Other definitions for aesop that I've seen before include "fabulous figure?" , "Fabulous writer" , "A pose of famed fable teller" , "Greek fabulist (Tortoise and the Hare)" , "satirical writer" .)