A sculpted head is recovered from an ancient ruin. Not much of the face remains; its features are now a field of broken stone. The biographer works like a restorer, an archaeologist salvaging and piecing the past together. The seams of historical construction always show. Only the novelist pursues the pretense of flawless history.

Certain biographers, like Edward Renehan Jr. in “The Dark Genius of Wall Street: The Misunderstood Life of Jay Gould, King of the Robber Barons” (Basic Books, 352 pages, $30), balk at their genre’s fragmentary nature and try to bootleg the omniscience of fiction into biography. Here, for example, is how Mr. Renehan handles the fact that Jay Gould’s father, John, had three wives who died on him: “Perhaps thinking himself cursed, John did not take any more wives.”

This is the kind of idle speculation that gives biography a bad name. Men tended to go through wives at a rather rapid rate in the 19th century. Why would John feel especially cursed? Perhaps he was a doomsayer; perhaps not. “Perhaps” is the only word that rescues the biographer from falling entirely into the realm of fiction.

Fortunately, Mr. Renehan does not indulge in this kind of factitious filler often. Indeed, it is his mission to present Jay Gould’s life by chiseling away at the encrusted myth that has elevated Gould as the cyclops of American capitalism, a monster who had an eye only for making money.

To be sure, Jay Gould was a “dark genius of Wall Street,” but not the dark genius, as his latest biographer contends. Plenty of other men – Vanderbilt and Rockefeller, for example – engaged in cutthroat monopolistic practices. And Gould was no inhuman engine of financial predation. He managed many of his businesses well and made good profits for his stockholders. He was well read in literature, and he wrote well. He loved to garden, and flowers gave him a sense of exquisite joy. He was a family man who cared deeply for his children and was devoted to his wife. He was charitable, often supporting good causes anonymously, and – the claims of other biographers notwithstanding – Mr. Renehan demonstrates that Gould was able to make and maintain many friendships.

So what accounts for the legion of reporters and biographers who deemed Gould a fiend whose theme song, in the words of “Cabaret,” was “money money money money money!” I am ashamed to say that my own fraternity – the brotherhood of biographers – has not done its homework. Some, like Edwin Hoyt, wrote nearly pure fiction, as Mr. Renehan, a demon researcher, demonstrates.

Even if you are not especially interested in Jay Gould, Mr. Renehan’s biography is an eye-opening lesson in how a biographical myth is fostered in order to further the biographer’s own biases and desire to entertain readers. Mr. Renehan might have added that the 19th century was the Great Age of the American Stage Melodrama, the time of Simon Legree and the Count of Monte Cristo, who emerges from the sea to mount a fake rock to proclaim, “The world is mine!”

Newspapers, including The New York Sun, simply invented copy about Jay Gould when they could not find the real thing. The Sun, in fact, predicted divine retribution for Gould (a kind of editorializing no longer in fashion). Yet 19th-century readers craved such stories when reading about robber barons – a phrase popularized by Gould’s most famous, if not most accurate, biographer, Matthew Josephson.

“But wait!” you say. Surely Gould deserved infamy. He tried to corner the gold market and drove the country into a financial panic. He invented the sort of financial chicanery the SEC was created to police. Mr. Renehan would not disagree with you. As he points out, Gould was a genius at identifying the precise point in financial transactions when the most money was to be made.

Early on, Gould made a small fortune in the leather trade – recognizing, as he wrote his father, that it was not the tanners but the merchants “who command the true power of the industry.” If Gould stood out from most other capitalists, it is because he was consistently innovative – sometimes acting in concert with his financial partners, sometimes cutting them out of the action when he wanted to seize an opportunity immediately.

I direct you to Mr. Renehan for more details about how to become a Jay Gould. My biographer’s curiosity is drawn instead to what Mr. Renehan makes of the man himself. How did Jay Gould feel about his own reputation? The well-read Gould quoted Machiavelli to a friend: Better to be feared than loved. It was good business, in other words, to be perceived as the evil genius of Wall Street. In fact, Gould was not always successful. He made bad investments, his biographer shows – including those that resulted in tremendous losses when he attempted to corner the gold market.

Gould wanted the public to believe he was a Mephistopheles and that his businesses could not fail. Near the end of his life, he regretted that he could not leave a better name for his progeny to bear. By then, however, he was a captive of his myth. If he gave significant sums to charity anonymously, it was because on those occasions when his donations became public, Gould was ridiculed as attempting to salve his conscience (an odd accusation, since the devil by definition does not feel guilt).

There is one other point Mr. Renehan might have emphasized even more than he does: Gould was a man in a hurry. He had a weak constitution, and several members of his family had died of tuberculosis. He did not expect to live long. Descriptions of him in his mid-40s emphasize premature aging. Given his immense labors and long hours at the office, it is surprising that he made it to 56, and he knew it.

I suspect Gould felt he did not have the time to be overly scrupulous. But, then, I am speculating, in danger of veering off into that land of fiction that beckons biographers so enticingly.