"I have seen Elvis in the supermarket," the letter said.

It was sent from Bay City, Michigan, to the columnist Ann Landers, who published it in 1988. Landers had been inundated with mail from readers about Elvis Presley sightings after writing in an earlier column that she believed the official account of Elvis' death.

Elvis, who would have turned 80 today, has been dead for almost as long as he was alive. He was 42 when he collapsed at his Graceland home in August 1977. The conspiracy that he didn't actually die that day has persisted ever since, underscoring his mark on American culture in a way that says as much about Elvis as it does about the American identity.

After all, conspiracy theories are almost always about more than denial. Some scholars believe that they're a way to question power structures. "Recent work on conspiracy theories has borrowed from Marx’s theory of alienation to argue that such narratives emerge at times when individuals feel powerless, disadvantaged, or voiceless," wrote Viren Swami, a professor at the University of Westminster, in a 2012 Frontiers in Psychology paper. To understand what questioning the narrative about Elvis' death has to do with power structures, it helps to understand what he meant to people.

"He stood for rock 'n' roll at a time when rock 'n' roll was rebellion, but I think Elvis stood for so many more things than that," said John Covach, a professor of music theory at the University of Rochester's Eastman School of Music. "He was a southern kid, so he came from very humble roots. He became very popular and very rich and very famous. In this country, that's the American Dream. And that's the Elvis story."

It makes sense, then, that so many people reported seeing Elvis in places that are overwhelmingly American. In Kalamazoo, Michigan, in the late 1980s, an account of Elvis ordering a Whopper at Burger King set off a rash of sightings. And in the nearly four decades since his death, people have claimed to see him at grocery stores, 7-Elevens, shopping malls, and fast-food chains, ordinary places frequented by regular folks—not the sort of setting where you might expect to bump into a rock star.

Elvis was known to have had some of the eccentricities that superstardom encourages. My father, who worked as Elvis' security detail at what was then a Hilton hotel off the Las Vegas strip in the early 1970s, remembers hearing of hotel staffers carrying a replacement television set to Elvis' hotel room—after Elvis put a bullet through the screen of the television that was already there. Apparently he didn't like what was being broadcast. His nickname—the King—was a reminder that Elvis was extraordinary, not just among regular Americans but among other musicians, too. And yet he was able to stay relatable in a way that other celebrities could not.

The items he famously insisted be stocked at all times in his Graceland kitchen, for instance, sound like things you'd find at a Fourth of July barbecue in the 1950s. On that list, according to a 1993 Associated Press article: hamburger buns, pickles, ingredients for meatloaf, brownies, vanilla ice cream, chocolate ice cream, mustard, peanut butter, Juicy Fruit gum, bacon, Pepsi.

Elvis grew up in a small Mississippi town and served in the Army. He may have been a sensation, but he was able to retain the boy-next-door quality that made it seem natural for a nation of fans to call him by his first name. In the popular imagination he was always both a rock star and a regular guy—conflicting qualities that helped the eventual conspiracies about what happened to him flourish. Today, these questions of identity are inextricable from the larger cultural idea of Elvis—so much so that you can't really talk about Elvis without, in the same breath, talking about not Elvis. There's the man who died, and the man who pretended to. There's the man who maybe faked his death, and the legions of fans who dress up like him.

For the generations born after Elvis peaked, the lookalikes are more familiar than the actual musician. The twilight of the 20th century was awash in Elvis impersonators, Elvis sightings, Elvis memorabilia. Until recently there was a roadside museum devoted not just to Elvis but to challenging the story of his death—called, of course, the Elvis Is Alive Museum—in Wright City, Missouri. (Its curator told The New York Times in 2007 he planned to sell the museum's artifacts on eBay.)

"It is true that once a person's image has this link to popular culture, sometimes they can feel like they are as disassociated from that image as the image is from reality," Covach told me. "[The Beatle] George Harrison once said something like, 'I see these pictures of myself in the paper, and I read these things I said. And when I am looking at it, it seems like I am looking at a different person.' I think what he's putting his finger on is that once a media image emerges, it kind of takes on a life of his own.

"It's almost as if you realized you had a double, like in that Dostoevsky story. That's what your image is—it becomes this double. It's appropriated by the culture and sometimes you can be really disturbed by what it ends up being and standing for. The Elvis everybody thinks they know is probably not the real Elvis. It's Elvis the icon, only sort of tangentially linked to the reality."

The tricky thing about Elvis, though, is that people can't agree on the Elvis they think they know. There's the Elvis who died in 1977, and the Elvis who's still alive and eating cheeseburgers in western Michigan. There's Elvis the hip-swiveling hunk who could break your heart, and Elvis the doughy 40-something who couldn't get through a performance without stumbling over his words. This duality was strong enough that it prompted debate about which Elvis ought to be depicted on a postage stamp. From The New York Times in 1992: "Postal authorities are not sure which Presley likeness to use: the young, svelte, hip-gyrating Elvis of the rock-and-roll '50s, or the rotund, road-worn Elvis who died in 1977 near the end of the Age of Aquarius, reportedly after a struggle with drugs."

If conspiracy theories are a way to impose order on events that can't be controlled, Elvis sightings are perhaps a way of rejecting mortality, and preserving the American dream he came to represent. After all, it wasn't just Elvis' death that challenged his place in American culture, but his actual life. Insisting Elvis never died is also, then, a way of rejecting what he had become.

"It is a kind of romantic idea," Covach told me. "This idea that maybe Elvis was just tired of the limelight—and he was starting to get old and he was starting to get overweight—and he decided to fake his own death so he could live anonymously without the glare of the photographers. That seemed attractive to people."

Like the letter writer from Bay City, Michigan, who claimed to have encountered Elvis in the supermarket on more than one occasion. "Once he gave me a wink as if to say 'Don't tell anybody.' Several people in Kalamazoo know where Elvis lives, but they respect his privacy and are protecting him from the media."

"So much of what he stands for is resonant with a lot of things people like about the American tradition," Covach told me. "Sometimes it seems like it's about Elvis, but it's really about something much bigger."