Literary musketeer (5)
I believe the answer is:
athos
'literary musketeer' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for athos that I've seen before include "Dumas musketeer" , "Greece's holy mount" , "Colleague of Porthos, Aramis" , "Literary musketeer" , "Greek mount; one of the Three Musketeers" .)