J. R. R. Tolkien's Lord of the Rings is a massive epic fantasy of more than a half-million words. It is also a hugely complex work, with its own complicated chronology, cosmogony, geography, nomenclature and multiple languages, including two forms of elvish. The plot is so grand, moreover, that it casts backward to the formation of first things while glancing forward to the end of time. How did this huge and learned work—written by an obscure Oxford philologist—become a classic?

The answer has to do with Tolkien's central characters. They are humanoid creatures called hobbits, and their unlikely hero has the unheroic name of Frodo. During the 1960s, so many American youths...