The Hobbit actually predates the Trilogy by about 17 years or so...when he began writing about the One Ring, it wasn't until later that he made the correlation between it and the magic ring Bilbo 'found' in Gollum's cave.
Anyhow, the Rangers are known as Dunedain, or Men of the West; Aragorn and his people are special in that they are the direct lineal descendants of the Numenoreans, or First Men as they are also known. In a word, their bloodline is pure and unbroken from father to son over a span of thousands of years. A singular form is 'Dunadan' or 'Man of the West'.
I also read most of the companion research novels that were written by Tolkien and/or his grandson, Christopher...a wealth of information is contained in 12 volumes known as the History of Middle Earth. Given the Trilogy, the Hobbit, these volumes and others such as the Silmarillion (which reads much like the Bible in certain aspects) and you can almost understand how these words still carry so much weight nearly a hundred years after they were first imagined.
The movies were great, but they left a lot out and changed a few points...to no detriment of the film itself but there's so much more to the source material. Not for everyone as it was mentioned in another thread about the pacing of the novels...they do go into detail and I know there are some out there who would have difficulty following along when some of the more expository chapters are in play.
