What significance does Granger have in Ray Bradbury's novel, Fahrenheit 451?
In Ray Bradbury's Fahrenheit 451, it is not until the story's end that Montag meets Granger.
When Montag kills Beatty, he is forced to run for his life: the Mechanical Hound is after him and—if he catches Montag—will use his needle to inject Montag with drugs and kill him. In fleeing, Montag knows he must cross the tracks and find the river. The water will help confuse the dog's ability to track a human's scent.
When Montag reaches the water, he meets Granger, another of the people fleeing from the repressive society in which they live. Granger gives Montag a drink that will further destroy the Hound's ability to find him. Granger speaks to Montag of the importance of reading, learning and memorizing books, and then passing them to other who will do the same. Whether books are burned or not, the knowledge will not disappear. The age-old "oral tradition" is seen here, used thousands of years ago to pass on stories and history when people did not read or write, and/or had no materials to write with.
Granger then introduces Montag to a number of the book people and explains to him how they keep the books alive by memorizing books or parts of them in order to preserve and hand them on to others. By using this oral tradition, the book people feel the content will not be lost, even if all the books are burned.
With a mechanical device Granger has, he allows Montag to view the authorities' pursuit to capture him, as well as the war that breaks out, and the bombing and destruction of society as they know it. However, Granger is also optimistic that Granger, Montag, the book people, and others like them will help society to rise from the ashes like the mythological Phoenix who lived for hundreds of years, was destroyed in fire, but was able to regenerate and begin a new life, rising from the fire's ashes. This is the dream that Granger shares with Montag at the story's end.