The specter of biography has long struck fear in the hearts of living legends. Martha Washington, Henry James and Somerset Maugham tried to thwart would-be chroniclers by pitching private papers into the fire — heartbreaking acts of futile resistance. Trusted correspondents did not, as James instructed, “burn, burn, burn.”

Charles Dickens, however, had a much happier outcome in his friend John Forster’s three-volume biography, published between 1871 and 1874. The trouble, according to Helena Kelly’s new book, “The Life and Lies of Charles Dickens,” is “simply that Forster wasn’t a very good biographer.”

For decades Forster, a writer and critic of comparatively modest success, was kind of like Dickens’s literary companion. He listened to Dickens’s troubles, read his rough drafts and negotiated much of his life, including a marital separation from Catherine Hogarth, the mother of his 10 children, whom he left for Ellen “Nelly” Ternan, an actress 27 years his junior. It was the first time Dickens — who was “astonishingly, globally famous,” Kelly writes, “a product, a brand” — suffered in the public eye.

And before he died, in 1870, Dickens entrusted Forster with his manuscripts. Ever the “faithful assistant,” Forster copied down “the story Dickens gave him,” and published the first volume of “The Life of Charles Dickens” 18 months after his subject’s death, which is the best time to make hay.

A century and a half later, archives are far more accessible than they used to be, and Kelly is ready to try “Dickens the conjurer” for a book that amounts to “posthumous brand management.” Among a laundry list of perjury charges is Forster’s biggest revelation: that the novel “David Copperfield” was semi-autobiographical, inspired by Dickens’s childhood labor in a boot-polish factory during his father John’s (first) stint in debtors’ prison. Dickens, who wrote his own press releases, had managed to suppress the most basic facts about his background; now readers had Forster to “confirm” what they’d suspected all along.

“The picture of the young Charles as an inexplicably neglected child labouring forlornly in a warehouse by the river while his father languishes in the Marshalsea prison is terribly affecting,” Kelly writes, “but can we be sure that it’s accurate?” This is not a new question — nor is it one the author ultimately answers. In an 1872 issue of The North American Review, a critic called the fib “a good example of this peculiarity of Dickens’s character, and of Mr. Forster’s apparent inability to detect it.” In fact, many of the inconsistencies, omissions and outright lies Forster parroted have since been corrected and refined; and Kelly — an Oxford Ph.D. whose previous book was “Jane Austen, the Secret Radical” — is noticeably ungenerous with her citations, which mostly include 19th-century sources, conspicuously omitting the generations of scholars who’ve come before her to illuminate Dickens’s dishonesties.

When Kelly unleashes her inner literary critic, she delights readers with pages upon pages illustrating the enduring influence of Dickens’s fictional biography on his fiction: The prisoner John Barsad returns to his family in “A Tale of Two Cities”; the orphan Esther Summerson buries a doll that is a vestige of her former life in “Bleak House”; the titular “Little Dorrit” is born and raised in Marshalsea.