Robert DOUGLAS-FAIRHURST, the Oxford scholar who is one of Charles Dickens’s two new biographers, rightly calls his subject “at once the most central and most eccentric literary figure” of his age, and the investigations into the dark corners of that eccentric life began with Dickens himself. In 1849 he showed a short account of his early years to his close friend John Forster, revealing a story he never told his own family: the shame-inducing months he spent, while his father was in a debtor’s prison, as a 12-year-old “laboring hind” in a factory that bottled shoe-blacking. The first volume of the biography he’d wanted Forster to write — which made the ­blacking-factory episode public — appeared in 1872, two years after Dickens died at the age of 58, and its successors keep coming. The Dickens biographies published just in the past 25 years make an impressive stack. Given his uncanny genius and the vivid complexity of his life, that’s not a complaint.