They are people Bradbury refers to as "book covers". They each have memorized a book and plan to store the information for future generations that will need it. They think they are essential to society because they are the last carriers of the information stored in books that society used for so many centuries. Without any one of them, a huge information gap would form that could never be restored. No book can be rewritten in its original form; therefore, these people hold the last link to the invaluable knowledge contained in the books. This group hides out in the mountains until the bombing is over, and then it is up to them to re-enter society and pass on the knowledge they have acquired.
In Part Three of Fahrenheit 451, Montag meets a group of men in the woods. These men consist of former college professors who are ostracised from society because of their opposition to censorship. Their leader, Granger, for example, struck a fireman and has been running ever since.
Each man has memorised a book and, often, at great risk to himself: some have undergone plastic surgery, for instance, and others have had their fingerprints altered.
According to Granger, these men do not consider themselves to be important, as he tells Montag:
Hold on to one thought: You're not important. You're not anything.
Instead, Granger believes that these men are simply "remembering" knowledge and that, one day, this knowledge might be called upon by the next generation:
They weren't at all certain that the things they carried in their heads might make every future dawn glow with a purer light.
These men, therefore, function as symbols of hope: their future role may be uncertain but it is tinged with optimism.