In early 1964, the Scottish-born photographer Harry Benson was getting ready to head to Kenya to cover that country’s first few months of independence when he was abruptly pulled off the assignment.

Instead, in what surely qualifies as one of the more serendipitous disappointments in a photographer’s career, London’s Daily Express told him he was being sent to Paris to follow an up-and-coming Liverpudlian pop group called the Beatles.

Benson would be there the night Beatles manager Brian Epstein burst into their hotel room with the news that “I Want to Hold Your Hand” had landed on the top of the U.S. charts. It would be Benson who prodded John, Paul, George and Ringo to start a pillow fight (much to John’s chagrin), and it would be Benson who snapped the famous black and white photo of the four lads tussling playfully in bed just a week before they made their historic first trip to America.

The pillow-fight image is among several iconic Beatles shots, including one of the quartet camping it up with Muhammad Ali (then still known as Cassius Clay), that are part of “Harry Benson: Being There,” the first major U.S. museum retrospective of Benson’s work, which was organized by the Scottish National Portrait Gallery and opens Friday at the National Portrait Gallery in Washington, D.C.

A quick stroll through the exhibit offers a dizzying array of the luminaries and high-profile moments captured by Benson, whose skills were honed during his days as a Fleet Street tabloid photographer in the 1950s and 1960s. Benson, it seems, has an uncanny knack for not only making sure he is everywhere at the right time but also for taking the definitive shot of whomever he is covering.

For instance, Benson, the only photographer with the Beatles on their inaugural flight to the United States, uses his lens to peer into the glassy eyes of a tearful Pat Nixon as she watches her husband resign the presidency; to memorialize the raucous cheers of a group of well-heeled English boys meeting the arrival of Winston Churchill on his final visit to his alma mater Harrow; to meditate on the painter Andrew Wyeth as he contemplates the water, sketchbook in hand, at his Maine retreat; and to crystallize the gorgeous Jackie Kennedy popping out of her sister Lee Radziwill’s London front door. The list goes on and on.

Benson has photographed every U.S. president since Dwight Eisenhower, and he’s skilled at tricking insight out of his time with the commanders in chief. That said, the political pictures included in the show almost always illuminate some essential aspect of the men who have held the post.

Benson’s portrait of President Bush, taken in 2000 when the then-presidential candidate was still governor of Texas, comes about as close to summing up the man as any in recent memory. Here is Bush at the Governor’s Mansion in Austin seated on a fancy Victorian sofa, leaning in intensely like an excited cowboy watching a rodeo from the sidelines, a fist clenched in exhortation. Bush is all Southern good ol’ boy save for an oddly contemporary circle-patterned tie. Benson had told Bush he’d recently become an American citizen shortly before the photo shoot, and, according to Benson, Bush had retorted: “Well that means you can vote and I’m asking for your vote.” Bush, the presidential candidate, is in full-on selling mode.

Other Benson photos delve into the relationship between presidents and their first ladies.

Most famous, of course, is the shot of Ronald and Nancy Reagan (in black tie) dancing across a white backdrop in the White House Map Room en route to a state dinner. (Again, their “moment” had been prompted, in this case by the sounds of Frank Sinatra’s “Nancy With the Laughing Face.”) Nancy Reagan, in a black sequined gown, stares adoringly at her man and gives a feminine kick of the leg. The picture’s presence on the cover of a 1985 issue of Vanity Fair is singlehandedly credited with turning around that magazine’s then-dismal fortunes.

But it’s Benson’s photographs of civil rights leader Martin Luther King Jr. and then-Sen. Robert Kennedy (D-N.Y.) — both of whom were assassinated — that are among the most arresting in the exhibit. First, there is a photo of King in the throes of an impassioned moment not long after activists in the 1966 March Against Fear had been tear-gassed. Fast-forward a few years later to the stoic faces of King’s wife and children as they arrive in Atlanta for his funeral, and finally to an image of the slain civil rights leader’s head peeping out of his casket.

For sheer terror, however, nothing really competes with Benson’s pictures of then- presidential candidate Robert Kennedy. A buoyant Kennedy is seen marching in the 1968 St. Patrick’s Day Parade in New York, then a few months later, a triumphant Kennedy at Los Angeles’ Ambassador Hotel is shown addressing supporters after winning the California Democratic primary. From there ensues a series of increasingly horror-filled shots — Kennedy’s felled body, then a panic-stricken Ethel Kennedy desperately lurching at Benson with an outstretched hand as she tries to push him back from her shot husband, then a young, freshly disillusioned campaign worker standing watch by the bloody spot of Kennedy’s assassination, then a lonely pool of blood marked only by a leftover political hat. Finally, mourners are shown lining the tracks where the train carrying Kennedy’s body from New York to Washington was due to pass through. The detail in that last picture is so perfectly framed, there’s even the cross-like post of a power line hovering elegiacally in the background.

The photographer earned his share of criticism for the images, said the show’s coordinating curator Ann Shumard, noting the “unease” some of the Kennedy pictures created when they were published. There were “questions” whether they were appropriate, she said. Nevertheless, Benson felt it was his role as a photojournalist to record the moment, she added.

Benson, who has worked for publications such as Life, People and Vanity Fair, has never been content to stay “behind the ropes” with the other photographers, Shumard said. He had that “slightly different take on American life because his roots were elsewhere,” she asserted, noting that his Scottish “charm” hasn’t “hurt him one bit” when it came to coaxing his subjects.

It’s probably no surprise then that he’s adept at depicting unabashed glamour in a quirky, insouciant manner. For instance, in one photo, Truman Capote in a scarf and sunglasses frolics on the dunes. In another, the director Roman Polanski (now a fugitive) buried in sand up to his neck screams for help in the face of an unexpected wave. (It was Benson who put him there in the first place in the course of a pirates-and-buried-treasure photo shoot for French Vogue.)

And Benson also peels off the surface glamour to catch some of these celebs at their most vulnerable.

Elizabeth Taylor, her stitches still visible on her shaved head, is pictured in a hospital bed after an operation for a brain tumor. Her only company: a small, white dog. In another shot, the Duke and Duchess of Windsor look away from each other. The Duchess, the American divorcée for whom the Duke had abdicated the throne, is polished and aloof, while the former King Edward VIII looks spent, his mismatched clothes only serving to emphasize a general air of defeat. The couple seems as much exiled from each other as from the British throne.

Among Benson’s seemingly endless parade of the fashionable and the powerful, there also are a handful of quiet, more anonymous individuals represented here. We see a black man with downcast eyes sitting alone in National Airport with an American flag in his lap, having just finished burying his son who died in Vietnam. The subject is so utterly isolated in his grief, it’s hard not to want to cry for him even across the distance of nearly four decades. In contrast, Benson’s 1965 shot of a woman dressed in a white Ku Klux Klan hood nursing a baby elicits a more ambivalent response. Her face may be awash with the glow of unconditional love, but her attire is all hate.

“Harry Benson: Being There” runs from April 27 through Sept. 3 at the National Portrait Gallery, located at Ninth and G streets Northwest. For more information, go to www.npg.si.edu.