I did all this for the same reason de Kooning spent a year attempting to distill Kennedy’s essence — because like many others who have written about him, I was gripped by the challenge of creating a definitive portrait of one of the most complicated, secretive, elusive and enigmatic men ever to occupy the White House, and of solving what I consider the greatest Kennedy mystery of all: not who killed him 50 years ago, but who he was when he died.

Even those who knew Kennedy well have spoken about the seeming impossibility of knowing him in his entirety. Ted Sorensen , his principal aide and speechwriter, believed that “different parts of his life, work, and thoughts were seen by many people — but no one saw it all.” A former Cabinet member called him a “very introverted man” who “kept a lot of things to himself.” His close friend Charlie Bartlett, who had introduced him to Jackie, said, “No one ever knew John Kennedy, not all of him.”

Even Jackie threw up her hands, calling him “a simple man, yet so complex that he would frustrate anyone trying to understand him,” and concluding that “to reveal yourself is difficult and almost dangerous” for people like the Kennedys. “I’d say Jack didn’t want to reveal himself at all.”

For a Kennedy biographer, comments like these are like a red flag to a bull.

One of the greatest challenges Kennedy poses to anyone writing about him is that, because he rigorously compartmentalized his friends and family members, their impressions and recollections of him are sometimes at odds. He was intellectually closer to Sorensen than to any other adviser, yet the two men did not socialize, and the president never invited Sorensen to the intimate dinners at the White House family quarters at which former Washington Post editor Ben Bradlee was a frequent guest. Bradlee says he knew nothing about Kennedy’s energetic philandering, yet Kennedy’s trusted secretary Evelyn Lincoln knew about his womanizing and in at least one instance offered her home address so he could receive letters from a mistress there.