This summer, at literary festivals and bookstores around the world, readers celebrated the 20-year anniversary of the debut of the first book in J.K. Rowling's Harry Potter series — "Harry Potter and the Philosopher's Stone" (re-titled "Harry Potter and the Sorcerer's Stone" in the United States) — and with good reason. Since the young wizard's first appearance on June 26, 1997, the "Boy Who Lived" has become the "Icon Who Endures."

Over the past two decades, the Harry Potter series has expanded to include seven novels, with a total of 450 million copies in print, including translations into more than six dozen languages. The eight films spawned by the books have grossed $7 billion, with toys and merchandise garnering another $7 billion.

That is why it is startling for me to recall the sour reception that my students gave "Harry Potter and the Sorcerer's Stone" in fall 1999, when it appeared on the syllabus of my Princeton University course on popular literature, American Best-Sellers. A survey of popular writing from the 17th century to the present, the course invites students to consider how and why particular best-selling works have captivated their audiences. At the end of each term, I let the students select the final book as an exercise in popular taste. In 1999, they chose that first Harry Potter novel.