Possible Clues:

• Friend of Aramis
• Literary dueler
• Royal guardsman taking out the French from parapet openings
• Dumas dueler
• Literary musketeer
• One of the Three Musketeers
• One of a French literary trio
• D'Artagnan cohort
• Classic role played by Gérard Depardieu in 'The Man in the Iron Mask'
• Colleague of Athos, Aramis