The African-American businessman William Ellis, pictured here around the year 1900, frequently passed as Mexican. COURTESY FANNY JOHNSON-GRIFFIN

Some people knew him as William Ellis, and others as Guillermo Eliseo. He could be Mexican, Cuban, or even Hawaiian, depending on whom you asked. Everyone seemed to agree that he was spectacularly wealthy and successful. In the dime-store Who’s Who books that were popular at the turn of the twentieth century, his name, in one form or another, appeared regularly. He was a “Banker, Broker, and Miner,” who came to New York from the “Mexican frontier,” an exemplar of the self-made man.

It was one of his life’s many ironies that the pedigreed gatekeepers of American high commerce celebrated his origin story without knowing a thing about his actual origins. William Ellis was born a slave, in Texas, in the eighteen-sixties. Like at least some of his siblings, he was light-skinned, but with a key difference: on the city census that recorded blackness with a “c” (for “colored”), Ellis was somehow spared the label. In his early twenties, he got into the cotton trade after a brief apprenticeship with a white local businessman, shuttling back and forth to the cities in northern Mexico. He started telling people that he was Mexican, and that he had anglicized his name for their convenience, as Karl Jacoby recounts in his fascinating new book, “The Strange Career of William Ellis.” Having grown up just south of San Antonio, along the border, Ellis came to speak fluent Spanish. He quickly grasped the possibilities of bilingualism in the race-riven landscape of the Reconstruction-era South.

Throughout the nineteenth century, and well into the twentieth, the porous border with Mexico blurred the stark dividing line between white and black in America. In 1850, in Texas, there were twenty-five thousand “Tejanos”—that is, American residents of the state who came from Mexico and spoke Spanish. The U.S. had acquired a large swath of the borderlands from its southern neighbor two years before, so a certain haziness was inevitable. In 1857, a runaway slave named Dolores Brown argued in court that she was born south of the border, “upon the Guadalupe River, of Mexican parents.” Unable to prove otherwise, the judge had no choice but to pronounce her “a free person of Mexican descent.”

Three decades later, twenty-four-year-old Ellis was living in San Antonio, striking out on his own in the cross-border trade, when he decided to get involved in politics. Doing so risked revealing his true identity, but he was convinced he could walk a fine line: advocate for a cause without being defined by it. In increasingly prominent ways, he fought for black representation in the local Republican Party. At rallies, he delivered impassioned speeches that caught the attention of the local press, which praised his rhetorical flair. At first, the papers referred to him as “Mexican Ellis” or “W.H. Ellis, from Mexico.” But before long he was being described by some of them as a “colored aspirant for legislative honors.” His allies eventually lost their bids for control of the Party, and Ellis suffered a kind of double defeat: both a political setback and personal exposure. “It was a gamble that had not paid off,” Jacoby writes. For a while, he had to lie low.

He resurfaced in the papers a few years later, this time as the leader of a daring new experiment. He wanted to relocate hundreds of black Americans living in Alabama to a colony in northern Mexico. The country, he told prospective colonists, “is better known as the country of ‘God and Liberty,’ and . . . offers unequaled inducements for agricultural laborers in the growth of cotton and corn.” It was mainly a business proposition, but he couched it as philanthropy—“the greatest opportunity ever offered to the colored people of the United States.” There was an additional perk in it for Ellis. In Mexico, he could finally be himself as an American. “He never passed as a Mexican while south of the border. Rather, he took pains to emphasize his U.S. citizenship, which, together with his position as a well-connected businessman, gave him a certain cachet at a time when Mexico avidly courted foreign investors,” Jacoby notes.

The project was an unmitigated disaster. The living conditions were uncomfortably reminiscent of those on the antebellum plantations, and rumors spread that Ellis was making a profit on the backs of the workers, which was partly true. The whole failing scheme sank Ellis’s reputation, irrevocably, in Texas. In April, 1898, when the San Antonio city directory was published, Ellis’s name had a “c” next to it for the first time in his life.

And so he moved to New York. At the time, forty-two per cent of the city’s residents were foreign-born. Ellis shifted cannily between different identities, trading on the baseline anonymity afforded by the big city. “The task of passing, especially in our great cities, is not so difficult as is supposed,” a writer going by the name Heba Jannath wrote, in an essay titled “America’s Changing Color Line,” in 1934. (Jannath, ironically, was actually a pen name adopted by a white writer, Josephine Cogdell. Cogdell, who was married to the black journalist George Schuyler, published the piece in “Negro: An Anthology.”) Some sociologists have estimated that as many as twenty-five thousand black Americans tried to pass under a different race each year during the early twentieth century.

The Mexican and Cuban populations were still relatively small in New York, even as Manhattan-based capitalists looked increasingly toward markets in the Americas. This gave Ellis greater leeway; there wasn’t a well-defined Hispanic community or identity that could mark him as an outsider. Over the course of Ellis’s lifetime, the U.S. dramatically redrew its relationship to Mexico: in 1880, annual trade between the two countries was fifteen million dollars; by 1910, it was a hundred and sixty-six million. Ellis’s strategies for passing were also good for business: his Spanish and his border bona fides were, finally, a kind of credential.

He married a white woman, who called him “Gerry,” her diminutive for “Guillermo.” (She seemed never to fully know, or at least acknowledge, his backstory.) In New York, their children grew up in an all-white neighborhood of Mount Vernon (nicknamed the “City of Happy Homes”) and identified as white. Ellis’s business interests grew more conventionally capitalistic—he invested in mines and water companies—with his bounty rising and falling by the vicissitudes of the market. When he attempted to lead a diplomatic delegation to Ethiopia, he was greeted warmly, but as an American businessman rather than a black internationalist. It was a stunning mark of his perennially double-edged success. “Ellis’ business empire was too intertwined with American empire for the two to be completely disentangled,” Jacoby writes.

One of the most dramatic scenes in Jacoby’s book describes a train ride that Ellis took back to New York, after one of his trips to Mexico. It was in March, 1909. “A tall man with penetrating brown eyes and carefully groomed mustache, attired in the latest fashion—spats, top hot, tailored three-piece-suit, gold watch chain and jeweled fob draped across a powerful barrel chest—caught the eye of authorities in Eagle Pass,” Jacoby writes. He began the journey in a country free of segregation laws, only to cross into another that had them in full force. As soon as the train edged over the border, a question arose: “What race was he?”