In J. R. R. Tolkien's legendarium, the Rangers were two secretive, independent groups organized by the Dúnedain of the North (Arnor) and South (Gondor) in the Third Age. Like their Númenórean ancestors, they appeared to possess qualities closely attributed to the Eldar, with their keen senses and ability to understand the language of birds and beasts. They were great trackers and hardy warriors—defending their respective areas from evil forces.
The two groups of Rangers were the Rangers of the North and the Rangers of Ithilien. The two groups were unconnected to each other, though distantly related by blood.
Tolkien's Rangers (and Aragorn in particular) are the primary inspiration for the Dungeons & Dragons character class called "ranger".