HALF a century ago this month, four young musicians from Liverpool introduced themselves on a US television show.
That was all it took for millions of music fans across the States to fall in love with the Beatles.
Their electrifying appearance on the Ed Sullivan Show on February 9, 1964, in front of a screaming audience and some 73 million people watching at home, paved the way for Beatlemania to sweep North America.
Last week, the two surviving Beatles, Sir Paul McCartney and Ringo Starr, led a star-studded rendition of the classic Beatles song Hey Jude in Los Angeles as they marked the 50th anniversary of that epic performance.
The band may have broken up in 1970 but they remain a formidable money-making enterprise. Their musical heritage - their unrivalled back-catalogue, consisting of dozens of the finest pop songs written - has been exploited skilfully. That music, after all, defined the 1960s and helped change a generation.
The 50th anniversary is being marked by the CD release of the US versions of Beatles albums put out by the Capitol record label in the 1960s. Moreover, many younger fans are continuing to discover the Fab Four for themselves.
McCartney, now 71, shows no sign of slowing down, and both tours and records frequently.
According to the 2013 Rich List, he and his wife Nancy Shevell have a joint fortune of £680 million, with all but £150m of that attributed to McCartney. His 2012 On The Run tour grossed $57 million from 18 dates.
In 1980, he was estimated to be worth £80m. According to the US website Celebrity Net Worth this week, his net worth is now reckoned to be $800m.
Reports last August claimed that he could, within five years, win back the publishing rights to the Beatles' songs. The rights were bought by the late Michael Jackson in 1985.
Starr, who is now 73, made profitable tours in both 2012 and 2013, was reckoned by the 2013 Rich List to be sitting on £160m.
The Beatles' main company, Apple Corps, reportedly paid £18m in fees and dividends in 2010-11 to McCartney, Starr and the families of the late John Lennon and George Harrison, though only £1.6m in 2011-12.
So why do the Beatles remain so relevant and profitable in 2014?
"It falls into two categories -the music and the business side," says Martin King, director of The Beatles Story, the award-winning visitor attraction in the band's home city of Liverpool.
"When they broke up in 1970 they didn't go into hibernation. They all had great solo careers and they've all had best-selling solo compilation albums. The Beatles' number ones sold millions, too.
"John, before his untimely death in 1980, had seven albums with hits.
Paul has been incredibly prolific and he picked up a Grammy lifetime achievement award last weekend and also an award for best rock song with the members of Nirvana.George had a dozen solo albums. Ringo had hit albums and, like Paul, continues to tour.
"It's these world tours that help account for the fact that The Beatles are growing across the globe. There's even a tribute band in China."
KING added: "It's fabulous for me running The Beatles Story, where I can see that the band has cross-generational support.
"It's not just the baby-boomers like me who grew up in the 1960s, and for whom they were both a music phenomenon and a social phenomenon, who love the Beatles."
The two remaining Beatles are also doing well in growth markets such as Latin America and China.
"So they've kept their music and their fan-base going, but you could say the same, too, of several other bands who began in the 1960s. But what marks the Beatles out is that they have any number of timeless songs with broad appeal.
"In many ways, The Beatles are to music what Citizen Kane is to films.
"If you look at all the polls of the best-ever albums, they usually feature more than just one Beatles album.
"You'll get Sgt Pepper, Rubber Soul, Revolver, Abbey Road and The White Album on these lists."
Like many baby-boomers, King plays the Fab Four's music at home and in the car, where his "relatively young" children have grown to love the Beatles as much as more current chart music.
The Beatles Story has enjoyed a 10% year-on-year growth and King, like other authorities on the Beatles, has spotted signs of a fresh surge of Beatlemania because of the 50th anniversary celebrations.
Apple has made an astute job, he said, of controlling the band's brand - the back-catalogue and logos for licensing.
"They've often said 'No'. You won't find the Beatles on 1960s compilation albums, although you'll find everyone else. So when their songs appear on iTunes, it's a big thing. When they launched their own Anthology documentary in 1995, with accompanying CD and book, it was a big thing.
"If we were talking about business and marketing, it would be about brand management, though they might not even call it that.
"Even if Apple Corps is controlled by lawyers and accountants on their behalf, the surviving band members and the spouses of John and George are making quality decisions."
There is no reason to suspect the cross-generational love for a band that broke up 44 years ago will fade, with King predicting the Beatles could remain a 22nd-century phenomenon, "in whatever form music is played in then".