When I set out to write a book about Las Vegas’s golden age of entertainment, in the 1960s, I discovered that I was venturing into largely forgotten territory. There are plenty of books about Las Vegas—the hotels, the gambling, the Mob—but few that focus on the entertainment itself, the history and evolution of the Las Vegas show.

Elvis Presley quickly took over the book and proved the perfect framework for it. He first appeared in Las Vegas, few remember, in 1956, when he was just breaking out (he hadn’t even appeared on The Ed Sullivan Show yet), and Colonel Parker booked him into the New Frontier Hotel, on a bill with Freddy Martin’s orchestra and Shecky Greene. The engagement was a misfire: the Vegas nightclub crowd didn’t know what to make of this hip-shaking rock ’n’ roller. But Elvis loved Vegas. He got friendly with Liberace (who told him his act needed more glitz), and he returned there often for R&R. He shot Viva Las Vegas there in 1963. He married Priscilla at the Aladdin Hotel, in 1967. And so it was fitting that, when Vegas was starting to flounder in the face of the late-60s rock revolution, it would turn to the original rock ’n’ roller as the agent of its re-invention.

What struck me most about Elvis’s great comeback show in 1969 is how much of a homemade, seat-of-the-pants production it was. For his high-stakes return to live performing after nearly a decade away from the stage, Elvis didn’t have a director, a hands-on producer, or even a Vegas or music-industry guru to rely on for advice. He put the show together largely on his own, with the help of a couple of friends. He picked the backup musicians and singers; chose the songs and organized his set; and resisted the Colonel’s effort to mount a traditional Vegas show (Elvis surrounded by showgirls), instead creating something new for the city: not an intimate, Rat Pack–style nightclub show but a big, rock-concert-like extravaganza. It was the starting gun for all the changes that would turn Las Vegas from a gambling-and-nightclub town for adults into the theme-park, family-vacation mecca that we know today.

When Vegas started to flounder, it would turn to the original rock ’n’ roller as the agent of its re-invention.

I was surprised at how much I came to admire Elvis as a person. For all the craziness of his world—the entourage of sycophants, the drug-fueled decline of his later years—people liked Elvis Presley. I interviewed dozens of former friends, fellow musicians, and showbiz acquaintances, and I can honestly say that I didn’t hear a single disparaging word. (That is rare, for a biographer.) He was unfailingly polite, modest about his fame, generous to friends and fellow performers, a good listener, an avid reader, an easy laugh. For a kid from Tupelo who had to deal with the kind of frenzy-inducing fame that really had no precedent in American popular culture, it’s amazing that he stayed as grounded as he did, for as long as he did. His comment after meeting the Beatles, a group he both admired and envied, was telling: “There’s four of them,” he told a friend. “There’s only one of me.” And that was not a boast.

Richard Zoglin is the author of a biography of Bob Hope, Hope: Entertainer of the Century, and Elvis in Vegas: How the King Reinvented the Las Vegas Show, to be published by Simon & Schuster on July 23.