On or about December of 1835, in a gallery in Boston, Massachusetts, used for the display of freaks, machines, and oddities, American pop culture officially began. Virginia Woolf first made the historical arrogance of such a statement possible in her famous declaration that “on or about December 1910 human character changed,” though the very definition of human was still in question in the summer of 1835. This was when the notorious P. T. Barnum—father of American sideshows, founder of the American Museum, and progenitor of the modern circus—“bought,” or acquired, the rights to display the slave woman Joice Heth from an itinerant showman named R. W. Lindsay.

So-called nursemaid to George Wash­ington and property of his father, Augustine, this slave was said to be 161 years old, with skin so dark and textured with age that it was impossible to doubt its longevity and hard not to see the gnarled past in it. She had witnessed the nation’s birth, the billing claimed. Word was she had secrets about those origins and would gladly share them with whoever came close enough for her near-blind eyes to confirm the will to believe. Though a slave, this creature had helped make the country possible by being mammy to its epic hero: democracy incarnate, its contradictions intact. Touch her.

The claim that she was 161 years old came from either Barnum or Lindsay. Barnum would eventually suggest that it came from Heth herself, for reasons obscure to him but which nevertheless impelled his trust, as only slaves could in a time when total subjection was imagined as purest affection.

Barnum’s ownership of whom or what he called “Aunt Joice” remains as unclear as the nature of their relationship. That relationship would transform from outright slavery to sideshow collusion and artistic collaboration; from the multiple exploitations necessary for carnival show business to Barnum’s eventual suggestion that it was Heth who duped him—America’s greatest con man—as he moved his spectacle from free states to slave states and from sideshows to museums in those years where the difference between the latter pair were as negligible as those between the former.

Their relationship got murkier in later years, as Barnum began to reinvent himself as something more than a confidence man, a huckster, a performer, a slave owner, and an entrepreneur. “Aunt Joice” became a ghost in his story just as Barnum became his own greatest creation. By then, Barnum could boast of being even more important than the great George Washington himself. He had, after all, pioneered a new type of celebrity—a sort that would make his beloved country always seem bigger than it was and more enduring than any of its...