Gunslinger

Oh God yes.

Historically, gunslingers were the rough-and-tumble frontier men of the old west, where, armed with the two most famous guns ever made, the Colt revolver and the Winchester rifle, they fought the natives, the animals, and one another in the name of Humanity Fuck Yeah.

Culturally, the gunslinger was the American equivalent of the old stories of the European knight-errant, wandering from place to place righting wrongs and shooting bandits. One famous aspect of these stories is the quick-draw duel, where two men stand in the street at high noon (when everyone knows to get out of the way and the sun is be in neither of their eyes), and stare each other down, each waiting for the other to draw first so that he will have the benefit of arguing "self-defense" in court after the duel is over. In most, but not every case, the villain draws first, but the hero is faster than him and kills him.

Just like the medieval knight underwent a series of anti-heroic revisions recently, the cultural myths around the gunslingers of the old west have been reexamined in a number of "revisionist" Westerns that paint them in a more morally-ambiguous light.

Pathfinder

Pathfinder actually had the balls to add gunslinger as a character class in a world of knights and swords, because fuck Medieval Stasis. They're built on the "fighter" template, so they get lots of hitpoints and lots of feats, and they enjoy a resource pool called grit that they can use for various effects. Grit is actually regenerated by doing badass deeds of derring-do more than by rest, so shooting out chandeliers, challenging villains to quick-draw duels, and leaping sideways through the air while firing are all heartily encouraged.

More than perhaps any other class, gunslingers benefit from Pathfinder's "archetype" system. One gunslinger class feature basically lets the character pick a gun off a rack to start the game with, and picking an archetype and picking an archetype to go with it is very advantageous. Musket master gunslingers get lots of free reloading powers, pistoleers get extra damage, artillerists get to be cannon fighters, etc. Note that there isn't really a good "holding a pistol in each hand" build, so it's probably best not to try.

Your firearm is your friend and your bosom buddy. You probably won't be starting out with a multi-shot firearm for balance, so making reloading as quick and easy as possible is absolutely paramount. Take the quick reload feat if your archetype doesn't already come with one, and take ranks and ranks of the Craft: Alchemical skill so that you can make your own alchemical ammunition, which, even when it doesn't have any special powers, further reduces the time necessary to reload a weapon. Getting it down to a free action by the time you can take multiple shots per round is important. Also, when you inevitably roll a critical fumble and your gun breaks, don't be stingy with your grit. Doing a quick clear may cost you time later, but it will save your goddamn life now.