It is widely accepted that the French Sharpshooter who fatally shot Vice Admiral Nelson was positioned high up in the mizzen-top of the 'Redoutable' which was locked in battle with H.M.S. Victory. Two Marines and one young Midshipman, John Pollard, brought up their muskets and then opened fire on the enemy rifleman with Pollard's musket ball finding its mark as the lone Frenchman fell down and toppled onto the hard, wooden deck below.
This little trio of British naval figures shows Pollard firing the fatal shot as two more 'Bootnecks'* back him up.

*'Bootnecks': A slang term for a Royal Marine, somewhat similar to the U.S.M.C. 'Leatherneck'. Both nicknames were derived from the leather stock once worn around the neck by the two different Marine Corps.