Born a slave near the Texas border with Mexico in 1864, Ellis triumphed over the entrenched racism of Gilded Age America by “passing” and becoming a rich entrepreneur in New York. To protect his new guise, however, he had to conceal his past, spread false stories, destroy documents and avoid photographers.

There are very few records about slaves or most freedmen, and little is known about Ellis’ origins: He had a number of (anonymous) white ancestors; his parents settled and worked in the town of Victoria in southeastern Texas, where he was born, and thus avoided the sharecropping fate of most African Americans in the region’s cotton-growing belt. Most important for his future was that he went to school and also picked up fluent Spanish.

Ellis’ facility with the language and an early job with a local merchant allowed him to enter into cross-border trade with Mexico, and by 1888 he was a dealer in “hides, wool, and cotton” in San Antonio. This is also when he first crossed a far more daunting divide and started calling himself Guillermo Enrique Eliseo: His appearance allowed him to claim that he was an ethnic Mexican and that his American name was a translation.

Subsequent attempts at passing became much easier, and soon Ellis was capitalizing on his business success, charisma and flair for language to begin a (brief) career in Texas politics.

But Ellis also had greater ambitions that were motivated in part by his desire to improve the lives of African Americans, whom he could not ignore even as he escaped their lot. In 1889, together with a partner, he signed a contract with the Mexican government to settle 20,000 African Americans in Mexico.

Unable to raise funds for this revolutionary plan, he tried again several years later, continuing to believe that emigration was the only solution to the race problem in the United States. The second colonization scheme did manage to settle some 800 African Americans in northern Mexico for a while before it also ended in failure.

Undaunted, Ellis reinvented himself once again, eventually landing in New York. His life became a kaleidoscope of entrepreneurial ingenuity, unrealized plans, dissimulation and, ultimately, unprecedented financial success. He developed a project for a railroad across Panama, bought a furniture company in Mexico City and became the Mexican representative for a French weapons manufacturer.

He claimed that he was from Cuba or, briefly, from Hawaii, and that he had helped Cubans revolt against Spain. By 1899 he had become the president of a corporation worth millions, with interests in reservoirs, pumping stations and real estate, and offices on Wall Street next door to the era’s premier investment firm of J.P. Morgan and Co.

Shortly after marrying a white woman (and inventing a story that she descended from English nobility), Ellis outdid himself yet again by hatching an extraordinary plan to head the economic development of Ethiopia. He made two trips to Addis Ababa, met the emperor and succeeded in attaching himself to an official American government mission to Ethiopia. Upon his return he debriefed the State Department and President Theodore Roosevelt at the White House.

However, by 1906, the Ethiopian plans had collapsed and Ellis’ situation began to deteriorate because of financial and legal problems. He continued to invent new schemes for lucrative deals in Mexico, but revolutionary turmoil there eliminated the connections he had long cultivated. Unable to find a solution and his health deteriorating, he died in Mexico City on Sept. 24, 1923, surprising his wife by leaving only $5,000 to her and their children.

Because Ellis was mostly successful in concealing aspects of his past, this elegantly written book is actually both less and more than the biography of a remarkable man, which also makes its title somewhat misleading. Not only are there gaps in the information about Ellis, but Jacoby often has to speculate about what happened to him or what made him tick.

And although Jacoby’s inferences are entirely plausible, what we get in the end is more like a fascinating silhouette of Ellis than a fleshed-out portrait. This is not for Jacoby’s lack of trying: he is a professor of history at Columbia, and his notes and bibliography run to more than 75 pages. To supplement his story, Jacoby broadens his focus from one forgotten individual to a “larger account of the evolution of the US-Mexican borderlands.”

Thus we also get a fine-grained history of the region and of related developments in the two countries, as well as illuminating surveys of the complex social, economic, demographic and — inevitably — racial issues that affected black and white Americans and their Mexican neighbors. Any biography must include such frames, but Jacoby’s are so wide and intricately carved that at times they overshadow his hero.

As Jacoby suggestively puts it, Ellis’ “passing” bears the “hallmark of the trickster from African-American folklore — charisma, deflection, improvisation.” Ironically, these traits are also what allowed Ellis to become that American ideal — a self-made man.

Vladimir Alexandrov is the author of the biography “The Black Russian.”