But in 1954, Jackson suffered a heart attack and died before he could finish this book. More than 40 years later, Robert Barrett, a law professor at St. John’s University working on a Jackson biography, received a call from Jackson’s family. They told him that Jackson’s son, Bill, had died, and that the relatives had found a manuscript in a closet in Bill Jackson’s Manhattan apartment.

Barrett read the pages and believed that he had struck historical gold. He decided that the book deserved to get published. In order to round out the portrait of FDR that Jackson was seeking to write, Barrett inserted excerpts from many other sources, including Jackson’s oral history and his unpublished autobiography. At times, these insertions disrupt the book’s flow. But on the whole, this is a winning memoir-the story of Jackson’s life in the White House; a powerful portrait of our 32nd president; and, most of all, a tribute to the humanity and the vision that stood at the heart of the Roosevelt administration.

Robert Jackson had a unique vantage point on his times. When he arrived in Washington in 1934, he took a job as general counsel at the Bureau of Revenue, the IRS’s predecessor. He rose rapidly through the ranks. He became the chief of the anti-trust division at the Department of Justice. He later served as solicitor general, then as assistant attorney general, and then as a Supreme Court justice followed by the capstone to his career-as the senior U.S. prosecutor at Nuremberg. One of Roosevelt’s close friends, Jackson played various roles in FDR’s White House: As presidential counselor and aide-de-camp, he served as an unofficial sounding board for Roosevelt’s ideas and strategies. Jackson had a hand in many of the most important debates of the 1930s and 1940s. He sent memos to the president, and he helped draft speeches and write messages to Congress. He took to the airwaves and the committee hearing rooms of Capitol Hill to defend Roosevelt’s policies and articulate his own views on the nation’s biggest issues. When he attacked the business tycoons who opposed the New Deal on the radio and in the papers, some of Roosevelt’s critics branded Jackson a socialist.

Jackson doesn’t shy away from discussing FDR’s shortcomings. He argues, for example, that FDR was weak when it came to administration. Roosevelt didn’t like to fire his aides, and he didn’t like to settle disputes between staff members. He had a habit of changing his mind depending on the views of the person who had talked to him last, and had a “happy disregard of channels, ranks and priorities.” While this often worked to his advantage, FDR occasionally infuriated bureaucrats with that same disregard. Lower-level officials were sometimes asked to intervene in matters where only the president had the authority to make a decision.

FDR once asked Jackson to settle a dispute over foreign financial policy between Secretary of State Cordell Hull and Treasury Secretary Henry Morgenthau. Jackson was shocked. “[It] would be impossible for me,” wrote Jackson, “to arbitrate between two men, both my senior in years, both my senior in Cabinet rank, both my senior in service there….” Jackson demurred. FDR “ultimately had to take up the task himself.”

That Man, in the end, is a strong endorsement of Roosevelt. It contains a trove of new information about Roosevelt’s life-his interactions with staff and friends, his habits when he was on vacation, his temperament and style away from the spotlight. The book also has some charming vignettes such as the one about a sailing trip through the Florida Keys. FDR had been ill, but once at sea, he began to relax. He caught mackerel and ate cooked fish for breakfast. He played nightly games of low-stakes poker and his luck, Jackson writes, was “phenomenal.”

“… [FDR] had rested. Life had been most informal in dress and in conduct. He was of course treated respectfully by all, but with perfect informality. In fishing contests, playing cards, and conversation, he was and wanted to be an equal. He asked no favors and granted none. He played the game on its merits. He was able to avoid all pose. He was away from curious eyes. We were completely isolated… It had been one of the delightful experiences of life.”

When Roosevelt died suddenly of a stroke on April 12, 1945, Jackson returned to the Department of Justice to eulogize his friend. Millions of people stood with FDR, Jackson told the audience, because “while he walked with Kings… he never lost the common touch; … he was their friend and advocate;… while he lived there would be no forgotten man.” Jackson predicted that long into the future, “The figure of Roosevelt will stand ‘like a sharply cut rock in the midst of a shapeless sea.’” That Man, after languishing in a closet for so many years, is a unique historical find and a ringing affirmation of that prediction.

Matthew Dallek, the author of The Right Moment: Ronald Reagan’s First Victory and the Decisive Turning Point in American Politics works as a speechwriter in Washington D.C.

Matthew Dallek, the author of The Right Moment: Ronald Reagan’s First Victory and the Decisive Turning Point in American Politics works as a speechwriter in Washington D.C.