FIFTY Million Elvis Fans Can't Be Wrong was the over-the-top title of Elvis Presley's 1959 greatest hits album, whose cover featured 16 images of the singer dressed in a gold lame suit made by tailor to the stars Nudie Cohn. It wasn't even the hip-swivelling chart star's first foray into greatest hits territory – that had come a year earlier with Elvis's Golden Records – though in its defence, Presley had reputedly sold at least that many singles by then so perhaps we can forgive the album title its note of bombast.

Today, however, could 50,000,000 Elvis fans even be found, far less judged to be right or wrong? And if not today, then how about on Wednesday, which marks the 40th anniversary of the singer's death?

Elvis Presley breathed his last on August 16, 1977 in Graceland, the palatial Memphis mansion he had bought in 1957. He died young in real terms but was old for a rock star whose executors found themselves with an icon to sex up and a reputation to burnish. Nor was his end one of those seedily glamorous deaths that had taken Jimi Hendrix, Jim Morrison, Janis Joplin and Brian Jones to early graves.

They all died aged 27, giving rise to the so-called 27 Club (later members would include Kurt Cobain and Amy Winehouse). Presley was 42 when he was found slumped in his toilet, and the official cause of death was given as heart failure though it was certainly exacerbated by years of abuse of prescription drugs and medicines. “Live fast, die young and leave a beautiful corpse” runs the famous line attributed (wrongly) to James Dean. Presley only managed the first of the three.

So the answer to the question posed above is yes – and also no. Certainly the thousands who'll flock to Memphis to take part in the annual Elvis Week's programme of events (highlights include the the Ultimate Elvis Tribute Artist Contest And Showcase) will view themselves as members of a millions-strong family of fans. So too will those who think tuning into a live stream of Elvis Week's all-night candlelit vigil is a worthwhile way to spend 12 hours. And so will the pilgrims who'll pay to stay at The Guest House At Graceland resort (it opened last year and features the largest hotel to be built in Memphis in nearly a century) or who'll queue to enter Graceland's latest blockbuster attraction, Elvis Presley's Memphis.

French fan Jocilyne Bellanttr, interviewed by an American news crew at the opening of the new $45 million, 40 acre visitor centre, probably speaks for many of those who treat a trip to Memphis as something akin to a pilgrimage. “When Elvis died, I said, 'Well my life is over, my fan club will close and I will be lost'. But after all these years I'm still here, my fan club is still big and it's a miracle. So to me, I'm living a miracle every day with Elvis."

Bellanttr's French Elvis fan club is one of around 400 still in operation around the world, according to The Elvis Presley Fan Club Of Great Britain, which was founded in 1957 and bills itself as “the world's most respected” Elvis fan club. It has around 10,000 members itself and some 300 are travelling to Memphis for the events marking the 40th anniversary of Presley's death. Multiply that by every other Elvis fan club worth its leather jumpsuits and, while it probably doesn't come to 50,000,000, you can appreciate how busy Memphis International Airport will be this week.

But anyone who experienced the visceral thrill of Elvis when he was at his most potent – the mid-1950s – would now be in their late 70s or 80s. So it's safe to assume that these Elvis fans are more recent converts, drawn not so much to the idea of Elvis the man as to the idea of Elvis the legend or even Elvis the dead showbiz icon. And what draws them to events like Elvis Week, what gives Graceland its title as the most-visited private residence in the world, what makes otherwise sane people fork out $20,000 for five nights in the light-filled Beverly Hills pad Elvis lived in between 1967 and 1973, is the lure of a very particular type of American celebrity – one built on graft and talent, but tinged with something darker and more tawdry.

More than that, these Elvis fans may be drawn to something they cannot quite explain. In his 1991 book Dead Elvis: A Chronicle Of A Cultural Obsession, hawk-eyed critic Greil Marcus dips into what he terms Elvis's posthumous “second life”, “a great, common conversation, sometimes a conversation between specters [sic] and fans, made out of songs, art works, books, movies, dreams; sometimes more than anything cultural noise, the glossolalia of money, advertisements, tabloid headlines, bestsellers, urban legends, nightclub japes”. In other words, an Elvis constructed from a tissue of supposition, wishful thinking, rumour, conspiracy theory – is he really dead? – and nostalgia.

One thing we can say with certainty is that even 40 years after his death, Elvis is a serious money-spinner. Elvis Presley Enterprises (EPE), founded in 1979 to manage Presley's estate, controls Graceland and its associated assets, of which Elvis Presley's Memphis is just the latest. EPE also controls all Elvis-related products, films, television shows, plays and musical ventures and is in turn majority-owned by Authentic Brands Group (ABG), a New York-based brand development and licensing company.

“We are brand owners. Curators. Guardians,” runs the spiel on the ABG website. “We build brand value.” Other icon-related “brands” in ABG's considerable portfolio include Marilyn Monroe, Muhammad Ali and Michael Jackson. In that sense, the King is in pretty good company – or Monroe, Ali and Jackson are, depending on how you look at it.

What people often forget, though, is the music. But the last few years haven't been short of weighty box sets to buff the legacy and Elvis completists still snap them up. In 2010, for example, The Complete Elvis Presley Masters was released, a 30 CD set containing all 711 official recordings Presley made. In 2016 a 60 CD box set titled Elvis Presley: The Album Collection was released containing all the material the singer released on the RCA label between 1956 and 1977.

And last month came a more manageable three CD set called Elvis Presley: A Boy From Tupelo – The Complete 1953-1955 Recordings. As well as a containing alternate takes, outtakes, live recordings and early interviews, it features a 120-page book and (get this) a week-by-week chronology of Presley's movements and activities in the period concerned. “Musical bedrock” was the phrase used by Rolling Stone magazine in a glowing five-star review.

The man behind that last release is Danish Elvis enthusiast and archivist Ernst Mikael Jorgensen. To his mind, you cannot over-stress the importance of Elvis Presley and he thinks that by reducing Presley's career almost to the length of a tweet – he was in the right place at the right time, made great records in the 1950s, some terrible films in the 1960s and then died in the 1970s from popping pills and gorging on burgers – “you skip most of what’s really interesting along the way”.

“I’m convinced that history needs to be told and retold and retold again,” he said in a recent Los Angeles Times interview. “If nothing else should come through, it’s that we don’t need to go back to [the idea that] Elvis got lucky. He didn’t just get lucky. Chuck Berry didn’t just get lucky. Little Richard didn’t just get lucky. They adjusted to a new form of music that wasn’t like any other form of music. They did something original, something that affected everything that came later.”

It's 63 years since Presley's first single That's All Right, a cover of a 1946 song by African-American blues artist Arthur Big Boy Crudup. “When you listen to that track now, you have to be reminded of how important, how groundbreaking it was,” said Jorgensen's collaborator on the A Boy From Tupelo project, RCA's John Jackson, in that same Los Angeles Times interview. “There was a lot of stuff released right around that time that sounds very similar, but to have that song, in that time, sung by that individual in that studio was one of the most important events of the 20th century. It set the stage for everything that followed.”

That's true. Nobody denies the effect Presley had on the musical landscape of the mid-20th century. But since his death, and despite the continual flow of boxsets repackaging his work, much of his musical legacy has either been obscured by the achievements of those who came after him or simply forgotten about. Elvis may still be The King, but it's not clear what he is king of or what his relevance is to many people under the age of 40.

Even 13 years after his death that was already starting to become the case. In a 1990 study of eight- and nine-year-olds conducted in a mostly white primary school in Tennessee and cited by Greil Marcus, English professor Charles Wolfe asked the question: do you know who Elvis Presley was? The answers are illuminating. “He was an old guy who was a king somewhere,” said one. “He lives in a big house in Memphis and he only comes out at night,” said another. “He was this guy who sang with his brothers Theodore and Simon,” said a third, confusing Elvis with Alvin, lead singer of 1950s children's novelty act The Chipmunks.

One problem for Presley's legacy as an artist is that he didn't write his own songs. He was given co-writing credits on a few of them, including Love Me Tender, though that was mostly at the behest of his grasping manager, the infamous Colonel Parker. And he certainly put his stamp on any song he recorded, even going so far as to tweak the arrangements. But for modern music fans in thrall to the cult of the singer-songwriter and desperately seeking authenticity in the cultural material they consume, it makes Presley a performer rather than an originator.

The fact that in his early career he often covered songs recorded originally by black artists doesn't help either. In the age of Spotify and iTunes, when virtually everything is available at the click of a mouse, why listen to Presley's versions of That's All Right, Hound Dog or Mystery Train when it's so easy to find the earlier, earthier, rootsier – and blacker – versions recorded by Arthur Crudup, Big Mama Thornton and Junior Parker respectively?

And while we're on the subject of anniversaries, last Friday's Google Doodle was an interactive celebration of the 44th anniversary of the invention of hip-hop – arguably a musical form which is more influential and meaningful today than the rock music that Elvis Presley originated. Ask a group of American eight- and nine-years olds today who Jay-Z is and they'd have no problem telling you.

Likewise, any young teenage rock fan in 2017 would recognise the cover of The Clash's ground-breaking 1979 album London Calling, with its famous picture of bassist Paul Simenon smashing his instrument. But how many would know that the design was a deliberate homage to Elvis Presley's equally ground-breaking 1956 debut album?

So back to the opening question: how many Elvis fans are there really and which Elvis is it they relate to? The Elvis that got fat and lost his way, becoming a befuddled, right-wing, anti-Black Panthers gun nut who genuinely thought Richard Nixon would/could make him an undercover agent for the Bureau of Narcotics and Dangerous Drugs? The Elvis that Andy Warhol turned into a rock and roll cowboy and potent symbol of American rebellion when he used a still from his 1960 western Flaming Star to make a series of Elvis screenprints, one of which – 1963's Eight Elvises – mimics that 1959 album in its replication of the singer's image? The Elvis that crooned and hollered on those wonderful early records while Scotty Moore threw out his inimitable guitar licks? The Elvis who played Vegas in a costume that would become the go-to garment for a generation of middle-aged impersonators? Elvis as Christ? As Satan? As Buddha?

The only answers about Elvis's appeal that Greil Marcus could come up with was that there was no answer, and that seems equally true in the 21st century. “There is a good deal in this book I cannot explain,” he wrote in an introduction to the 1999 paperback edition. “It's easy enough to understand a dead but evanescent Elvis Presley as a cultural symbol, but what if he – it – is nothing so limited, but a sort of cultural epistemology, a skeleton key to a lock we've yet to find?” Elvis made history, he states, but when he died “many people found themselves caught up in the adventure of remaking his history, which is to say their own”.

Here's a tempting line to end on, then: The King is dead, long live The King. But from a 2017 viewpoint, things aren't quite as simple as that. For a start, the king is dead and not dead at the same time – and even if his "second life" is as long as that hoary old proclamation wishes it might be, it'll unspool in a kingdom whose boundaries are continually being eroded and re-drawn.