Walter Isaacson explains in a brief subscriber-only essay on Time.com how he came to write an authorized biography of technology icon Steve Jobs:

In the early summer of 2004, I got a phone call from him. He had been scattershot friendly to me over the years, with occasional bursts of intensity, especially when he was launching a new product that he wanted on the cover of TIME or featured on CNN, places where I'd worked. But now that I was no longer at either of those places, I hadn't heard from him much. We talked a bit about the Aspen Institute, which I had recently joined, and I invited him to speak at our summer campus in Colorado. He'd be happy to come, he said, but not to be onstage. He wanted, instead, to take a walk so we could talk.

That seemed a bit odd. I didn't yet know that taking a long walk was his preferred way to have a serious conversation. It turned out that he wanted me to write a biography of him. I had recently published one on Benjamin Franklin and was writing one about Albert Einstein, and my initial reaction was to wonder, half jokingly, whether he saw himself as the natural successor in that sequence. Because I assumed that he was still in the middle of an oscillating career that had many more ups and downs left, I demurred. Not now, I said. Maybe in a decade or two, when you retire.

But I later realized that he had called me just before he was going to be operated on for cancer for the first time.

Isaacson also describes the last time he saw Jobs:

A few weeks ago, I visited Jobs for the last time in his Palo Alto, Calif., home. He had moved to a downstairs bedroom because he was too weak to go up and down stairs. He was curled up in some pain, but his mind was still sharp and his humor vibrant. We talked about his childhood, and he gave me some pictures of his father and family to use in my biography. As a writer, I was used to being detached, but I was hit by a wave of sadness as I tried to say goodbye. In order to mask my emotion, I asked the one question that was still puzzling me: Why had he been so eager, during close to 50 interviews and conversations over the course of two years, to open up so much for a book when he was usually so private? "I wanted my kids to know me," he said. "I wasn't always there for them, and I wanted them to know why and to understand what I did."

Isaacson's biography of Jobs is due to be out on Monday, Oct. 24. Simon & Schuster rushed the publication date from Nov. 21, as sales soared to make the 656-page hardcover the No. 1 bestseller on Amazon.