"MOST OF US SERIOUS collectors are normal, like everyone else," David Gainsborough Roberts was saying.

Not an electrifying observation, but I felt lucky to hear it, since gaining audience with an explorabilia collector had been so surprisingly hard. Through the dogged work of Helena Ingham, Christie's junior specialist for exploration and travel sales, my weeks of badgering for interviews finally bore results, and a few days after the auction I was patched through by phone to Roberts's home on the Isle of Jersey, one of the English Channel Islands, off the coast of France. "We're a tiny little island out here," he said. "But we have, let's say, more autonomy than the rest of Britain, especially with tax situations."

Roberts is a favorite of the Christie's staff, and he keeps several world-class collections going at once. A career private investor whose parents moved from England to Jersey in 1964, he's recognized as one of the planet's most ardent upscale pack rats. He's often brought in to assess new acquisitions for museums and private citizens.

"I have a lot of T.E. Lawrence's relics, his robes from the desert revolt, things like that," he said. "I've also got probably the world's best collection of Marilyn Monroe memorabilia. The only thing I truly lack is her dress from The Seven Year Itch. Debbie Reynolds owns that, and she's a very nice lady. Still, I've got the one from Gentlemen Prefer Blondes, and I'm a very patient man." Also in his larder: the clothes Bonnie and Clyde had on when they got gunned down by the law.

"Why do I do it? Why do I collect these things?" he asked rhetorically. "Well, I've always had a fascination with history. And these things, they link me to history—to real people, not some name on the page in a book. They were human beings, with frailties and personal pains and tragedies."

Roberts caught the fever early, as a child in England. "I grew up in a big old house with lots of attics," he said. "I remember my grandmother once coming to me with this six-by-four-inch piece of wood, and she said, 'This came from Lord Nelson's boat, the Victory.' And I recall thinking, Maybe Nelson trod on that. From then on, I was lost to collecting."

Roberts declines to name fellow collectors, saying only that most are intelligent, rich, and male. "But that doesn't exclude women," he adds, "or the gentleman in the row house who's saved for years in hopes a perfect object from some favorite old expedition might make its way to him."

In the end, Roberts says, "People who collect are searching for authenticity in a less and less authentic-seeming world. They want truth. Sometimes, alone in the house, I'll just go up to one of the bedrooms and pick up something from the collections. As I lift that thing, it still has that buzz of authenticity. It's electric. I can always feel it. It's funny, each time I buy something new, my friends all say, 'You could have had a week in Greece for the cost of that!' And I always respond, 'But I don't want a week in Greece. I want the buzz.'"