A pistoleer is a soldier trained to use a pistol, or more generally anyone armed with such a weapon.
The earliest kind of pistoleer was the mounted German Reiter, who came to prominence in Europe after the Battle of St. Quentin in 1557. These soldiers were equipped with a number of single-shot, muzzle-loader wheel-lock or Snaphance pistols, amongst the most advanced weapons of the era. Although mounted Pistoleers were effective against heavy cavalry, they gradually fell out of use during the Thirty Years War. After this time, cavalry in Western armies used swords or lances as their primary arm, although they still generally carried a pistol as a sidearm.
Horse-mounted pistoleers of a kind made a brief comeback in North America during the American Civil War (particularly by the Confederates) as well as in the conflicts against the Native Americans of the 1860s and 70s. This was a consequence of the adoption of the multi-shot revolver, which gave horsemen much more firepower.