Pronto

 is a slaver who works in Paradise Falls at a store called Lock And Load, repairing and bartering weapons and ammo. His repair skill is very low, usually surpassed by the players, so if you plan on spending a lot of time in Paradise Falls it's best to rely on the caravan merchants for repairs. His inventory is extremely limited, and can only be expanded by completing the unmarked quest Economics of Violence. If you ask Pronto in dialogue why his inventory is so bad, he will offer the explanation that his only suppliers are his fellow slavers, and they keep all of the "good stuff" for themselves. If you offer to help him, you will initiate the Economics of Violence quest.

Unmarked quest: Economics of Violence
You can expand Pronto's shop by giving him 20 Chinese Assault Rifles. In addition, he will get a bit more cash (around 400 instead of 150) and you will be privy to a 20% discount.

Appearances
 only appears in Fallout 3.