I love the Texas Rangers. They're just so hardcore! From a storytelling perspective, exaggeration seems unnecessary because these guys did it all. The Texas Ranger Division is a law enforcement agency based out of Austin created (unofficially) in 1823. It took another ten years for them to be officially recognized.
You have to think that in the mid 19th century communication between cities was not going to be fast, especially for an area of land as large as Texas (over 200,000 square miles). The area was developed by a hodgepodge of cultures (Spanish, Mexican, American settlers and Native Americans) and in dispute for quite some time. For over 200 years it was controlled by Spain. Then in a very short span of time it changed hands to the Mexican government, became its own Republic and then eventually joined the United States in 1845.
The culture in Texas was not exactly what one would call civilized. There's a lot of conflict arising for the various cultures and most cities were self-governed out of necessity rather than choice. A judge would have to be sent for in order to conduct a fair trail which meant there could be a delay of several days to several weeks. Frequently the occupants of a town took justice into their own hands.
The Texas Rangers were established to act like the FBI. They had jurisdiction over all of Texas rather than be limited by a city's limits. They were called in to solve crimes or apprehend criminals that were beyond what the typical town sheriff was capable of dealing with. This meant that they had to handle anything from murder investigation to riots to political espionage.
So you can image what type of a man it would take to work for the Rangers in the 19th century. He would be constantly travelling and would probably have worn an article of clothing until it disintegrated. Survival meant that he would have had to have been street smart and intelligent. He would have also had to be above average in weapon/gun skills. In my mind, these types of skills would have most likely been acquired from a hard upbringing.
Not a set of men you want to mess around with, basically. The Texas Ranger Division still exists to this day in a similar law enforcement capacity. Though I imagine today's modern day job has much better perks.