Animal backed by great fictional character (6)
I believe the answer is:
gatsby
'great fictional character' is the definition.
(I've seen this in another clue)
'animal backed by' is the wordplay.
'animal' becomes 'stag' (stag is a kind of animal).
'backed' shows that the letters should be reversed in order.
'stag' reversed gives 'gats'.
'gats'+'by'='GATSBY'
(Other definitions for gatsby that I've seen before include "Fitzgerald's great hero" , "Famous novel by F Scott Fitzgerald 'The Great . . . . . .'" , "Fitzgerald's Great character" , "great fictional character" , "Classic novel by F Scott Fitzgerald - 'The Great . . . . . .'" .)