In 1842, P. T. Barnum met a mermaid. She was just under three feet tall, with leathery skin, sharp teeth, and pendulous breasts. The mermaid had purportedly been caught by a fisherman off the coast of Japan. Mummified, she’d then been sold to an American sea captain. The sea captain tried to recoup the purchase price—roughly a hundred and thirty thousand dollars in today’s money—by exhibiting her in London, but the English papers were unkind. Soon the mermaid was second-billed to a “Learned Pig” named Toby. She fell into obscurity and then, eventually, into the hands of a Boston impresario.

When the mermaid was presented to Barnum, he was immediately taken with the shrivelled creature. The year before, he’d bought the American Museum, an establishment in lower Manhattan. It housed an eclectic collection of wax figures, statues, paintings, and animals both living and stuffed. Barnum’s chief interest in the venture lay, by his own account, in the “opportunities it afforded for rapidly making money,” and in the mermaid he saw a potential bonanza. The thing was an obvious fake—it had been stitched together out of parts of an orangutan, a baboon, and some kind of salmon—but that was a minor matter. How “to awaken curiosity to see and examine the specimen” was, Barnum said, “the all-important question.”

The scheme he came up with was to package one fraud inside another. Under a variety of assumed names, he composed letters to New York newspapers and arranged to have them mailed from cities including Montgomery, Alabama, and Charleston, South Carolina. The letters referred to a naturalist visiting from London, one Dr. Griffin, who’d recently procured “a veritable mermaid” from the “Fejee Islands.” Eventually, Dr. Griffin—actually, an associate of Barnum’s named Levi Lyman—checked into a hotel in Philadelphia, where he graciously invited a few journalists to view the specimen. Barnum, meanwhile, made the rounds of New York editors, complaining that his plan to exhibit the mermaid had been nixed by the fastidious Dr. Griffin. The woodcuts that he’d had made of the creature were now of no use to him, he said, so he’d allow them to be reproduced, free of charge. Three papers printed the images on the same day, each believing it had an exclusive.

“The mermaid fever was now getting pretty well up,” Barnum later recalled. When the specimen went on display at the American Museum, ticket sales tripled. Newspapers across the country printed notices about the “Fejee mermaid,” because, as Barnum observed, these “caught the attention of readers.” Thus the mermaid’s fame—and his own—“wafted from one end of the land to the other.”

Barnum lied easily and often. When he was not fabricating, he was exaggerating; he routinely inflated how much he’d spent on his various business ventures. He may or may not have said, “There’s no such thing as bad publicity,” but certainly he believed in this maxim and welcomed any imbroglio that would be noticed by the press. (Many times, he staged controversies for the express purpose of generating coverage.) He made a fortune, then lost it. While broke, he gave speeches on “the art of money-getting”; improbably enough, these proved extremely profitable. Toward the end of his life, Barnum toyed with the idea of running for President. His running mate, he suggested, should come from a state like Indiana. Barnum called himself the “Prince of Humbugs,” which, generously and perhaps presciently, left open the possibility that one day there would arise a king.

A new biography, “Barnum: An American Life” (Simon & Schuster), by Robert Wilson, traces the long arc of the showman’s career, which spanned most of the nineteenth century. According to Wilson, the editor of The American Scholar, Barnum’s peculiar gift lay in his relationship to his audience. Better than anyone who’d come before, the Prince of Humbugs understood that the public was willing—even eager—to be conned, provided there was enough entertainment to be had in the process. That theory of Barnum’s genius makes Wilson’s book peculiarly relevant, although it’s not altogether clear that this is the author’s intent.

Phineas Taylor Barnum—Tale to his family and friends—came from a long line of humbugs, Wilson relates. He was born in Bethel, Connecticut, in 1810, and named for his maternal grandfather. Uncle Phin, as the older man was known, had fought in the American Revolution and then managed to buy much of the property around Bethel. Growing up, Barnum was told that Uncle Phin had purchased a prime piece of farmland for him, a gift that made him the wealthiest child in town. Uncle Phin alluded to the purchase at least once a week, and Barnum’s parents, too, often mentioned their son’s good fortune. When, at the age of about twelve, Barnum was finally taken to visit—or, really, wade out to—his patrimony, he realized he’d been the victim of an elaborate prank: instead of fertile fields, he’d been deeded a hornet-infested swamp. If he was wounded by the hoax, he also seems to have profited from it. “My grandfather would go farther, wait longer, work harder and contrive deeper, to carry out a practical joke, than for anything else under heaven,” he later wrote. “In this one particular, as well as in many others, I am almost sorry to say I am his counterpart.”

In contrast with Uncle Phin, Barnum’s father, Philo, was a failure at money-getting, and when he died, in 1826, he left the family in debt. Still a teen-ager, Barnum was sent to clerk at a general store outside Bethel, where he staged his earliest recorded swindle. He advertised a “MAGNIFICENT LOTTERY!” and sold a thousand tickets at fifty cents apiece. Winners who came to claim their prizes received empty bottles or blackened tinware from the store’s inventory of old junk. Not surprisingly, the place soon closed.

Barnum tried opening his own store. He also founded a newspaper, the Herald of Freedom, and created an agency to sell lottery tickets. (This was long before government-sponsored gambling, and the contests were private ventures.) The store lost money. The Herald prompted several libel suits, including one that landed Barnum in jail. The agency, for its part, did quite nicely, until lotteries were banned by the Connecticut state legislature, in 1834.

The following year, Barnum finally found his vocation—or perhaps it found him. An acquaintance told him about a travelling act that was up for sale. It featured a woman, Joice Heth, who was advertised to be a hundred and sixty-one years old and the former nursemaid of George Washington. Barnum rushed to Philadelphia, where the show with Heth was playing. She was blind, toothless, and practically paralyzed. Still, as Barnum put it, she “was very garrulous when speaking of her protégé, ‘dear little George.’ ” He resolved to buy the act, which effectively meant buying Heth, who’d been a slave in Kentucky but whose legal status in Pennsylvania was murky.

In New York, Barnum engaged Levi Lyman, who later posed as Dr. Griffin, to serve as Heth’s director-cum-chaperon. The two men flooded the city with ads and, it seems, bribes; Lyman paid off editors to gin up interest. Whether or not New Yorkers were convinced by the claims made about Heth, they flocked to see her, and soon Barnum had made back the thousand dollars he’d paid for her. When the crowds in New York began to thin, he sent Heth and Lyman on to Providence, Boston, and Hartford. The abolitionist movement was strong in New England, so the flexible Lyman concocted a new story: the proceeds from the act were going to purchase the freedom of Heth’s great-grandchildren, back in Kentucky. Even by the standards of the time, Barnum’s use of Heth was shameful, a point made by at least one un-bought-off editor. A “more indecent mode of raising money than by the exhibition of an old woman—black or white—we can hardly imagine,” the Boston Atlas declared.