Most say the same thing. They came to the United States either to avoid army conscription or apartheid itself in the late 1980s. They planned to stay for just a few years, but they stayed on.

A quarter century later, this small generation of South African immigrants has risen to break through, en masse, into such key leadership roles that they're changing the US.

YouTube, PayPal, SolarCity, epigenetic cancer therapy and intelligent Mars robots exist only because of these expats: one of them has led the transition from PCs to cloud computing; another leads the US's top business school; and another is replacing the space shuttle.

But they've done it as individuals, and – with the notable exception of commercial spaceflight pioneer Elon Musk – almost invisibly.

In December, the Silicon Valley Business Journal made a remarkable statement regarding four of their first five winners of the US's high-tech chief executive officer awards, which feature competition from the likes of Google's Larry Page.

It said: "Here's something interesting about our executive of the year awards, something that hadn't occurred to us at the time that these four executives were selected – they are all originally from South Africa."

In Silicon Valley alone, South African-born high-tech chief executives include Vinny Lingham, founder of Yola and Gyft; Willem van Biljon, co-founder of Nimbula; and Pieter de Villiers, founder and chief executive of Clickatell, the world's largest online text messaging service.

And these weren't even among the award winners. Those include Gauteng brothers Lyndon and Peter Rive, who have built the US's largest provider of residential clean energy, and Paul Maritz, the outgoing chief executive of cloud computing giant VMware, who was schooled in KwaZulu-Natal.

Impact

South African immigrants in the US number only 83 000 – a "small number even for a big city", says Professor Nancy Foner, an expert on immigration achievement at the City University of New York.

So small, she says, that there are almost no figures or studies on their impact.

Yet new South African networking organisations, such as the Sable Accelerator in California, are springing up as South Africans are suddenly appearing in front of microphones as chief executives and university deans and scientific research team leaders.

Apart from well-established South African communities in places such as San Diego, or the tight group of professional golfers in Florida, South Africans don't network the way they do in the United Kingdom.

Instead, mutual recognition often happens like this: "Hey, that guy running the University of Notre Dame seems to have a Saffer accent. Come to think of it, so does the dean of Stanford Graduate School of Business. Ja, and what about the guy who was in charge of California's High-Speed Rail Authority? And with a name like Mahlangu-Ngcobo, that elections judge in Maryland has gotta be from home."

Some are fairly well known. Pik Botha's grandson, Roelof, has been ranked as high as 22nd on the Forbes Midas list of venture capitalists, ­having funded the launch of YouTube in 2005.

Among the celebrity conscription-dodgers, singer Dave Matthews probably heads the pack. Reportedly worth R2-billion, Matthews was recently declared the US's most successful touring act of the decade.

Remarkable anonymity

But most have risen to the cutting edge of American business with remarkable anonymity.

Former Illovo schoolboy Steven Collis, almost unnoticed, has taken the reins of healthcare wholesaling company AmerisourceBergen, listed 29th on the Fortune 500, with 13000 employees, and annual revenues of an almost ridiculous R600-billion.

It's the same story in science.

The single greatest breakthrough in cancer treatment in recent years – epigenetic therapy – has been credited to Stellenbosch's Peter Jones, who now runs a major research centre in California.

And another South African, Dr Liam Pedersen, has grabbed what could be the most exotic job in the US. He leads a Nasa research team to develop the brains of "intelligent" space robots that will explore the solar system in search of extraterrestrial life. And to test his "autonomous navigation" systems, Pedersen (42) gets to test the robots in places like Antarctica and alpine lakes in the Andes.

In terms of sheer impact for Africa among transplants, it's a draw between expats Dr Trevor Mundel and Nomvimbi Meriwether.

A former Soweto businesswoman, Meriwether – now owner of Meticulous Tours travel agency in Washington DC – is the co-founder of a multimillion-dollar health and basic education charity in Southern Africa, the Meriwether Foundation.

Astonishing over-achievement

She told the Mail & Guardian that her fundraising clout in the US enjoyed a major boost in December when her daughter – South African-born Nana Meriwether (27) – won the Miss USA crown.

"We are meeting governors, presidents, billionaires, so the plight of [South Africa's] most vulnerable ­children is being heard where it counts," she said.

Mundel, from Johannesburg, has been appointed as president of global health for the Bill & Melinda Gates Foundation with a grant budget of about R130-billion, and a brief of nothing less than to eradicate polio and malaria from the Earth.

But it's when you consider a professional field as specific as immigration law that the astonishing over-achievement of this group becomes clear. Bernie Wolfsdorf – another conscription dodger – has been named "the most highly rated immigration lawyer in the world" for the past three years by the peer-reviewed International Who's Who of Business Lawyers, and South Africa's Daryl Buffenstein is a former president of the American Immigration Lawyers Association.

In the same field, Chris Wright, a transplant from Johannesburg, is described as "Hollywood's go-to lawyer" – somehow securing "genius" work visas for everyone from Piers Morgan to Playboy playmate Shera Bechard. The "O-1" work visa is normally reserved for foreigners of "extraordinary ability", including Nobel prize, winners, but Wright has controversially expanded its use to include celebrities.

South African lawyers have not yet broken through, as a group, as judges in the US's highest courts, the way they have in, say, Western Australia. But Margaret Marshall (68), a former student leader at Wits, recently retired as chief justice of Massachusetts, where, in a landmark case in 2003, she was the first justice in the US to grant gay couples the right to marry.

Compared to the US's business world, expatriates have under­achieved in Hollywood itself, but its modest breakthrough artists include Charlize Theron, District 9's Sharlto Copley and Stelio Savante, who both co-produced and cracked a role opposite Matthew Perry in the comedy The Whole Banana last year.

Building and innovating

The poster-child for the 1980s immigration generation is Musk, the founder of Tesla Motors and SpaceX – the rocket company charged with leading the replacement of the space shuttle. In an earlier interview, he told me he left the country in 1988 because the South African Defence Force promised to be "an amazing waste of time".

He also said that South African TV was so bad in the 1980s that he was forced to read, and that off-the-shelf consumer options – such as amateur rocket kits – were so limited that he was forced to learn how to build and innovate on his own.

John Affleck-Graves, executive vice-president of Notre Dame, Collis and Wright were among those who told me they credit their education for much of their success, but offered few other clues as to why South Africans had risen so sharply.

Professor Foner says white South Africans, in particular, had "invisibly" risen to the top.

"South Africans [in the US] have gone unnoticed, especially the majority who are white, for whom there were few cultural barriers, if any," she said. "But I have noticed that South Africans move right into elite circles in the US, immediately, and look where they've gone."

Donovan Neale-May, founder of the Sable Accelerator, says the 1980s South African immigrant generation was unique in that they did not take advantage of contacts and mobility through "ethnic communities" in the US, "as, say, Indian entrepreneurs have done so effectively".

Instead, Neale-May says the conscription-avoidance generation had simply outcompeted American professionals with a multitasking combination of management talent, drive and pioneering vision.

Overwhelmingly white phenomenon

South African emigration to the US has been an overwhelmingly white phenomenon. According to the Migration Policy Institute in Washington DC, only 14% of South African immigrants – about 11 000 – are black.

And they've had to travel a far more difficult road, says Foner. Yet a number of black South Africans have made New World leaps that are, if anything, closer to the purest form of the "American Dream" than their rich white countrymen.

Among the exiles who remained in the US, Mahlangu-Ngcobo is one who has emerged as a national force in both government health policy and theology. She has testified on healthcare for the government's Congressional Black Caucus and, during the violent tumult in Liberia in 1997, she led a workshop there on violence against women.

The author of nine books – including research works on Aids and gender equality – Mahlangu-Ngcobo lectures on public health, and has founded both a US church and an international ministry.

Gift Ngoepe, the first black South African to be offered a professional baseball contract, is one of a more recent immigrant generation to the New World.

Unlikely sporting story

He discovered baseball when his mother took a job as domestic worker at the Randburg Mets clubhouse. A tiny room inside it later became his home, and he simply practiced against a wall until he was noticed by coaches and, later, a US mentor. Now, he plays professionally as a shortstop within the Pittsburg Pirates organisation.

Richman Mahlangu (49) has a similarly unlikely sporting story, but, in pursuing it, has carved out a classic, John Steinbeck-style American tale. He fled apartheid itself at the same time that Musk and others were ­fleeing conscription.

Mahlangu's "hook" into the US was a sports scholarship, after he literally discovered the sport of tennis when he found a broken tennis racket on a dusty street in Durban's Lamontville township in the 1970s. He says that, as with Ngoepe, a local professional coach was so taken by his diligent practice with that racket that he offered free lessons, and, eventually, an introduction to a US mentor.

Living in Las Vegas, Mahlangu has since achieved neither riches nor professional-level excellence in his sport. Instead, he has coached his two sons to the point where, last year, they were both recruited for scholarships by Ivy League universities. His youngest son, Yannik (17), has held a national rank of ninth for his age group and his eldest, Nicholas – now on his way to Harvard – has starred with Andre Agassi in a TV ad.

"For me, as an immigrant, this chance for my sons is my satisfaction," he tells me, in a line that could have been inscribed on Ellis Island.