If you haven't read Lord of the Rings, give up on life now
A race descended from the ancient kings of the Numenor, related to the Gondorians. Descendants of the Dunedain of the north, they survived by marriage with lesser men. Ruled by the line of Isildur, at the time of the war of the ring their leader was Aragorn son of Arathorn. Aragorn points out one time in Fellowship of the Ring that the rangers protected the Shire, Bree, and all the surrounding lands, so that the people there could remain innocent. This protection lasted for all of the third age.
Rangers are distrusted by those around them, as we see from Barliman Butterbur's reaction to Strider, AKA Aragorn. The distrust comes, at least partially, from the rangers' strange knowledge and their odd behavior. They tend to carry weapons, know how to use them, and worse, be involved with wizards and other unsavory types.