Robert A. Caro has reshaped both the concept and reality of political biography. In the four volumes of his biography of Lyndon Johnson, begun more than four decades ago, and in his earlier masterpiece, The Power Broker: Robert Moses and the Fall of New York, Caro has added dimensions to the study of monumental figures in American government and politics. He is owed a vast debt.

The 83-year-old Caro is now some 400 pages into what is anticipated to be an 1100-page, fifth and final, volume of The Years of Lyndon Johnson. There are fears among his global readership, including this writer, that he may not finish. Such fears appear to have crystallised in the author, for he has now published a memoir entitled Working: Researching, Interviewing, Writing. As Anthony Powell would observe, this work is a wonderful dance to the music of time.

Caro was brilliant in his appraisal of Lyndon Johnson's majority leadership in Master of the Senate, and then mesmerising in his minute-by-minute account of the then-vice president's experience in Dallas on November 22, 1963, The Passage of Power. A final volume will complete the magisterial work.

There is no question that Caro owes much of his success to his indefatigable researcher, his, wife Ina, who has ridden shotgun with him on this journey from New York City's South Bronx expressway to the hill country of Texas. At one point, Caro records, Ina sold the family home to ensure the impoverished Caros could keep writing.

No doubt also that a veteran editor, Alan Hathaway, on the newspaper News Day, contributed much to the depth of Caro's research. His advice still resonates:

"Just remember," he said. "Turn every page. Never assume anything. Turn every goddamned page."

There is no question that Caro owes much of his success to his indefatigable researcher, his, wife Ina, who has ridden shotgun with him on this journey from New York City's South Bronx expressway to the hill country of Texas. At one point, Caro records, Ina sold the family home to ensure the impoverished Caros could keep writing.

No doubt also that a veteran editor, Alan Hathaway, on the newspaper News Day, contributed much to the depth of Caro's research. His advice still resonates:

"Just remember," he said. "Turn every page. Never assume anything. Turn every goddamned page."

Caro took this advice to heart, resulting in both he and Ina trawling through voluminous files in Albany and New York covering the decades of Robert Moses' ascendancy. Hathaway's prescription was even more daunting when the custodians of the LBJ Presidential Library at the University of Texas in Austin told the author there were 32 million pages in the presidential archives.

But Caro has been fascinated not just by his protagonist and their careers but by the nature of political power in America itself. He explains:

"Every time an elderly man or woman, or an impoverished man or woman of any age, gets a doctor's bill or a hospital bill and sees that it's been paid by Medicare or Medicaid, that's political power. Every time a black man or woman is able to walk into a voting booth in the South because of Lyndon Johnson's Voting Rights Act, that's political power. And so, unfortunately, is a young man - 58,000 young American men - dying a needless death in Vietnam. That's political power... My books are an attempt to analyse and explain that power."

To trace and evaluate the marshalling of political power, Caro probes deeply into the lives of his characters. With Robert Moses, Caro traced the inspiration for his great highway and parks projects in New York City. From when Moses stood in 1914 on a Hudson River ferry with Frances Perkins (later to be FDR's Secretary of Labor) and imagined how the depressing mudflats on the Manhattan shoreline could be redeveloped with a highway project and related park amenities. We now call this place Riverside Park and the West Side Highway.

Meticulous research in the dusty and crumbling archives of the administrations of both governors Al Smith and Franklin Roosevelt of New York, saw Caro come across undeniable corruption on the part of Moses, building a freeway across the landed estates of the Long Island plutocracy. Among the great barons, Otto Kahn, protected his private golf course while small farmers saw their holdings shredded. Once Moses learned that Caro knew about the private donation of $US10,000 from Kahn for survey work, he refused all future interviews. Admirably, this did not cause Caro to divert or depart from his labours.

BJ caused Caro to dive very deeply into his personal and family circumstances in the Texas hill country. Astonishingly, the Caros lived among those who knew the Johnson family intimately and best for three years. This caused the normally taciturn Texans to open up in interviews. One memorable interview with LBJ's brother, Sam Houston Johnson, fundamentally altered Caro's understanding of the 36th President of the United States.

From a humble start working with fellow writers in the New York Public Library, Caro has become an acknowledged biographer of singular achievement. The US produces routinely presidential biographers of both integrity and perception. Robert Dallek, Doris Kearns Goodwin and David McCullough, among others, come to mind.

But only Carl Sandburg, with his two-volume biography of Abraham Lincoln and his three Pulitzer Prizes, comes close to Caro in terms of impact and appreciation.

For his contributions, Caro has won two Pulitzer Prizes and two national book awards. Former president Barack Obama awarded Caro the National Humanities Medal at a White House ceremony in 2010. This literary haul is well deserved.

It would be a tragedy if Caro does not finish the fifth volume of his biography of LBJ. Remarkably, he has mellowed in his attitude towards Johnson over the years of his writing. Caro was brilliant in his appraisal of Lyndon Johnson's majority leadership in Master of the Senate, and then mesmerising in his minute-by-minute account of the then-vice president's experience in Dallas on November 22, 1963, The Passage of Power. A final volume will complete the magisterial work. A more complete assessment of an American president may never be written. Working tells the tale of how the first four volumes have been written and how the fifth volume hopefully will be completed.