“Elvis has left the building,” is now part of today’s pop culture lexicon that alludes to the end of an event or concert. But when the phrase was heard on loudspeakers in the aftermath of the King’s comeback shows of the late ’60s/early ’70s, it usually meant Presley had been rushed into a waiting limo, cocooned inside a circle of men known as the Memphis Mafia — a squad of childhood friends and cousins who protected the singer’s every move. They remained with him from 1954 until his death in 1977.

Today, the job of protecting music celebrities has grown into a multimillion-dollar enterprise that embraces state-of-the-art technology and requires those involved to be highly trained professionals. The average platinum-level pop star employs a half dozen security pros around the clock, whose fees can range from $80,000 to $500,000 annually.

“It’s a different age now,” says James Andrea of RAD, one of the largest global music celebrity protection firms. “You have to be more in tune with technology; it’s much harder, especially with cameras and phones. There’s a lot you have to be on top of.”

RAD, started by Norman Oosterbroek, a Dutch security expert and former bodyguard to Nelson Mandela, touts a client roster that includes pop divas Beyonce and Lady Gaga; hip-hop superstars Jay Z, Drake and Kanye West; and record executive L.A. Reid. Like most professional security firms that protect music celebrities, RAD is tight-lipped when it comes to the specifics behind its operation. In most cases, artists make their bodyguards sign a confidentiality agreement to protect against tell-all books.

“Adaptability, in physical and psychological terms, is the main characteristic that you must possess,” says Julius De Boer, who was assigned by RAD to protect Beyonce and oversee logistics. “It is much more than being a human shield to your customer. You should always think three steps ahead, follow a schedule, and call ahead to destinations and so on.” Originally from the Netherlands, De Boer is fluent in five languages, giving him a distinct advantage when being hired by international superstars.

Nearly all who work in the field dislike the term bodyguard, since it implies a large, physical presence with the emphasis on brawn over brains. In reality, most security pros spend less than 20% of their time doing anything physical when protecting celebrities, and boast extensive training and college degrees. The majority of their time is either spent accompanying celebrities, or planning their safe travel, arrivals and exits from public appearances, meetings, performances, or simple, every day tasks such as shopping. Most of all, they protect their music superstars from the prying annoyance of overzealous fans and paparazzi.

“You have to advance every element,” says Andrea. “You have to know the precise spot where your vehicle will be parked and the best way to access or exit a building.” Pop’s biggest stars, such as Paul McCartney, the Rolling Stones, Bruce Springsteen, Madonna and U2, almost exclusively do what is known as “a runner” at the end of their shows. As soon as they finish, they are rushed into a waiting limo and whisked away, both as a security measure and to ensure they will not get stuck in a traffic jam.

Ringo Starr is usually being ferried by limo, accompanied by a police escort, to a waiting private jet while his band is still onstage performing the final stanzas of his signature encore, the Beatles classic “With a Little Help From My Friends.”

If Elvis was the first rock star to employ full-time bodyguards, the Beatles, during their touring years of 1962-66, were certainly the first group to demonstrate the need for professional security. Throughout this period, the Fab Four only had two security people, Mal Evans and Neil Aspinall, who also acted as the band’s roadies.

“It was a big thrill being young kids and being loved, or chased, by so many people,” said George Harrison, in a 1987 interview about the years of Beatlemania. “But, it became much more than any of us had ever dreamed of. … It just got to the point where it was making us crazy, so we had to draw the line somewhere. That’s when we decided to stop touring.”

Ironically, Harrison and John Lennon rarely used bodyguards after the band’s break-up; Harrison was nearly killed when attacked inside his home by a deranged, knife-yielding fan and Lennon was shot dead in 1980 outside the Dakota by stalker Mark David Chapman. McCartney, who still goes out in public without his bodyguards on occasion, was the target of Islamic extremists’ threats while touring Israel in September 2008. In order to ensure his protection, more than 5,000 security pros were hired for his visit.

Michael Francis — who has written a book about his years as a celebrity bodyguard for Frank Sinatra, Cher, Led Zeppelin, Bon Jovi and McCartney — says quality not quantity is rule when it comes to protection: “It’s an accessory now (when) you have to have four or five guys who weigh 400 pounds,” he says. “The big stars should have one good one that they trust.”

Francis handled incidents that included a gun being pulled on Bon Jovi in South America, and a deranged fan who entered the home of Cher at 4 a.m. wielding a samurai sword.

The rise in popularity of rap music also paralleled the rise of the modern security expert. Many of hip-hop’s biggest stars cultivated rap sheets in their rise to fame, which has led to a number of violent altercations at public appearances.

Many security pros have military or police backgrounds. Others, especially in the hip-hop community, have come from the streets, such as Jeff “Stretch” Williams, who confessed that, as a youth, had run numbers in Harlem. Williams cleaned up his act, joined the NYPD, and eventually worked security for P Diddy.

Kevin Hackie, former bodyguard of the late Tupac Shakur, recently admitted he was an undercover FBI agent while working for the rapper. Because of knowledge he reports to have, Hackie has been questioned in the murder investigations of Shakur and Notorious B.I.G.

A 2009 video shoot for rapper Busta Rhymes at a Brooklyn film studio ended in a hail of gunfire killing the rapper’s bodyguard, Israel Ramirez, when he attempted to escort extras and hangers-on off the soundstage.

“(Carrying a gun) is not a requirement, but many in this field do,” says Andrea. “Some of us are retired federal officers or police officers and they are already licensed to carry a gun. It is the preference of the client. It depends on the risk factor — if armed personnel are required, you get armed personnel.”

The topic remains timely. Warner Bros. Pictures recently announced it is doing a remake of the 1992 Kevin Coster-Whitney Houston film, “The Bodyguard.” Rihanna turned down the Houston role; but Miley Cyrus and Taylor Swift are reportedly still in the running.

One thing remains consistent: security pros believe diplomacy and restraint, above all else, are the keys to success in their business. “Physical force is never used or is always the last resort,” says Andrea. “Most of the time it is just a fan that wants to hug their superstar.”