Musketeer of fiction (5)
I believe the answer is:
athos
'musketeer of fiction' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for athos that I've seen before include "Literary musketeer" , "Greek mountain; one of the three musketeers" , "Greece's holy mount" , "Mount - musketeer" , "Brave soldier" .)