Pronto

 is a slaver who works in Paradise Falls, bartering and repairing weapons and ammo.

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

Appearances
 only appears in Fallout 3.