the npcs are the faceless masses. the ones who do the dreary day to day stuff - us in other words as we are in real life. in the game the players are the famous/infamous, apart from the politicians -as always they are a class of their own - so we are the sports stars, the people who explore and in later decades get books written about us, or who bounty hunt when the authorities cannot etc - who run the trade routes the npcs rule out as too risky.
so when you think of npcs, think of yourself in whatever nation you live in real life, and when you think players think of, i dont know, david beckham, pretty much any of the early apollo crews, chuck yaeger, arnold schwarzenegger, or josey wales, billy the kid, OJ Simpson. that kind of range of people. bat masterson, wyatt earp etc.