Other than the former president himself, no one likely knows more about Barack Obama’s life than David Garrow.

For more than 8 eight years, the Pulitzer Prize-winning historian has been toiling away at what will be the most comprehensive biography ever published on Obama’s life when it comes out on May 9. “This has been the whole last nine years for me, starting in early 2008 after Barack won the Iowa caucuses, and I concluded that having written so much on Dr. King and African-American civil rights politics, I should found out something about who this guy was,” Garrow said Sunday from his home in Pittsburgh in his first major interview about his book for “The Jamie Weinstein Show” podcast. “This covers everything from when his father leaves Kenya in the late 1950s, really up through 2016, though the book primarily focuses on the period up through 2007.”

Despite Obama being in the public eye for more than a decade, Garrow chuckles at the idea that there is little of significance left to learn about the former president.

“I think that people irrespective of their political views or partisan identification will be astonished—I cannot say that too strongly—will be profoundly astonished by how much important substance of Barack Obama’s life has not previously been known,” Garrow said.

Listen (conversation on his new Obama book begins at 45:36):

Indeed, Garrow is extremely critical of what he sees as the shallowness of the media’s coverage of Obama’s history.

“What most disappointed me back in the context of 2008 was how little interest U.S. journalists of all stripes took in the eight years that Barack spent in Springfield, Illinois, in the state legislature,” Garrow said. “There is not even, as we sit here today, a good magazine article out there about Barack’s time in the Illinois state legislature.”

Garrow is trying to keep a lid on most of the significant revelations in Rising Star: The Making of Barack Obama until closer to the book’s May publication date, but he did offer one major discovery.

“Barack and his closest friend in the early 1990s, when they were in law school, wrote several hundred pages of a proposed book manuscript that was never published,” Garrow said. “Particularly the 140 pages or so of that manuscript that are about race give significant insight into Barack’s thinking, you know, when he was leaving law school, about to enter into public life in Illinois.”

Asked whether any of the revelations in his book could have derailed Obama’s candidacy had they come out in 2008, Garrow said quite possibly.

“Had some Republican opposition researcher come up with” the book manuscript he wrote in law school, Garrow said, “there are multiple things that could have been used to Guinier him,” referring to how Republicans used controversial comments made in law review articles to derail President Bill Clinton’s nomination of Lani Guiner for assistant attorney general for civil rights in 1993.

“There are other examples,” Garrow added. “I think even back in 2008, 2009, from the very get-go, I was surprised at people’s willingness to assume that Barack’s memoir, Dreams From My Father, was without question historically reliable.”

“I thought from the beginning that that was probably too charitable a presumption,” he went on, hinting that his book will pick apart claims made in Obama’s highly praised post-law school memoir.

Garrow has met several times with President Barack Obama to discuss the book, though most of what went on in those conversations, he says, is off the record. Nonetheless, Garrow admits Obama “very strongly” disagrees with some of the claims he makes in the book.

“What I would fairly say, and we see this again very much in the present day, is that when one becomes president of the United States, it’s not uncommon for that person to think that their memory, their version of events, inescapably trumps all other people’s versions,” he explained.

But Garrow has done his homework. “I, all told, did more than 1,000 interviews for this,” Garrow said, noting the book is nearly 1,500 pages long. “It’s well over more than 200 pages of end notes,” Garrow pointed out. “The index, which was what I most recently had to sign off on, is 68 pages.”

In 1987, at the tender age of 33, Garrow won the Pulitzer Prize for his biography Martin Luther King, Jr. Thirty years later, with his massive tome on Barack Obama’s life, he just may nab a second by challenging what we know about America’s 44th president.