Johnson is one of the preeminent biographers of the twentieth century; his industriousness and thoroughness place him in the tradition of the multivolume writers of the nineteenth century who were his subjects. He began research for a biography on Sir Walter Scott in 1956, started writing in 1961, and ended up at the end of the decade with a manuscript of 500,000 words in 78 chapters. Sir Walter Scott: The Great Unknown (1970) was awarded the American Heritage biography prize in 1969, at $20,000 considered the largest award in the U.S. for a literary work. Some critics preferred Johnson's biography to Scott's works; all agreed that it was a definitive account of a major author. Johnson is… notable, also, as the biographer of Charles Dickens.