When Jack Kerouac read Neal Cassady’s spontaneous rush of words, he claimed it was more alive than any piece of writing he had ever seen. In its effusive style, its freewheeling candor, its Proustian (yes, Proustian!) introspection, the letter touched off a response in Kerouac that reshaped entirely his own approach to writing. The result was an explosion of “road” novels, beginning with “On the Road,” in which Cassady is renamed Dean Moriarity and seen as nothing less than “the root, the soul” of Beat legend.