It's never been so easy to become a billionaire – though it helps to come from a newly emerging economy and to be involved in an old-fashioned industry. And being under 60 is a big advantage.
In 1918, John D Rockefeller, the American behind Standard Oil, was the only member of the world's billionaire club and his $1.2bn wealth was almost six times as large as the next richest person's. Even in 1984, America had just a dozen people with 10-digit fortunes, but last week Forbes magazine put the US tally at 413.
But with almost 800 billionaires in other countries, the US is no longer the centre of world wealth. At the latest calculation, Russia boasts 101 entrepreneurs worth at least $1bn, but even that is beaten by China with 115.
Ten years ago, only eight Russians were on the Forbes list and just one person from mainland China – Rong Yiren, the chairman of the Citic Pacific conglomerate, whose assets were valued at $1.3bn. Only four Indians were on that 2001 list too, while now there are 55, with two in Forbes' top-10 – including Lakshmi Mittal, who runs his steel empire from London.
In 2001, there were only 538 global billionaires, most of them American: inflation and rising investment values have more than doubled that to 1,210. But, a decade ago, the tech bubble ensured entrepreneurs in the technology, media and telecoms industries dominated the Forbes list.
Media accounted for more than a fifth of the top-50 then, including names such as German television tycoon Leo Kirch and CNN-founder Ted Turner. Silvio Berlusconi was 29th on the list, worth $10bn, before he became Italy's Prime Minister. Now, media magnates account for half as many top billionaires, despite the growth of giants such as Google and the creation of Facebook.
Technology is still an important producer of billionaires, but they are growing more slowly. Bill Gates topped the list 10 years ago with his Microsoft colleague, Paul Allen, two places behind, followed by Larry Ellison of Oracle. Gates and Ellison remain in the top 10 – with only two other billionaires from the class of 2001 – but they have slipped, philanthropy has cut Gates's wealth from $59bn to $56bn.
They have been overtaken by Carlos Slim, the Mexican entrepreneur whose empire stretches from telecoms to financial services, retailing and much more. In 2001, his $10.8bn wealth made him only the 25th richest man in the world; last year, although already top of the list, he added another $20bn to reach $74bn.
Retailing remains a source of wealth, but even in this sector there are changes. Sam Walton, whose Wal-Mart group owns Asda, once regularly topped the Forbes list and his family remains well represented. But while even in the early 1990s the Sainsbury family was in the global top 10 just behind Bill Gates, David Sainsbury's $1.2bn only just got him into the top 1,000 this time.
Inside the top 10, ahead of the highest Walton, Amancio Ortega, the Spanish founder of the Zara clothes chain, represents the new face of retailing. Close behind are Karl Albrecht of Germany's Aldi supermarket group and Stefan Persson, the head of Sweden's H&M fashion group.
Oil used to be the route to making billions, and it explained most of the dozen billionaires in 1984; Five came from Dallas alone, many of them from the Hunt family. Yet a year later, when the oil price collapsed, the Hunt firms were facing bankruptcy and their owners were out of the lists.
Now, despite soaring oil prices, Saudi Arabia's Prince Alwaleed Bin Talal has slipped from sixth to 26th place as his $20bn value has stagnated, reflecting some poor investments in property and banking.
Indeed, apart from Warren Buffett, now 80 and holding his place one slot behind Bill Gates, finance provides few billionaires. George Soros scrapes into the top 50; US hedge-fund manager John Paulson is only just ahead of him. Financier Eli Broad made the 2001 list after selling his insurance firm to AIG.
And while Japanese real-estate investors topped the Forbes list two decades ago, property is another casualty of the latest recession, even if it does back Britain's biggest billionaire – the Duke of Westminster, whose $12bn (£7.5bn) places him at 56 on the list. The next best Britons are the Reuben brothers, also property investors, at 114 and retailer Sir Philip Green and his wife in 132nd position with $7.2bn.
As Western investors are pushed down or off the list – there are 56 fewer US billionaires than three years ago – those in emerging markets take their place. The Brics – Brazil, Russia, India and China – now boast more than 300 billionaire businessmen but their sources of wealth are not all software or technology but old-fashioned industries that the West has abandoned.
India's Lakshmi Mittal makes money from steel, Brazil's Eike Batista, another of the world's 10 richest men, makes it from mining and oil. While among the Russians, steel accounts for Vladimir Lisin's $24bn; Oleg Deripaska's wealth is based on aluminium; Vagit Alekperov owes his wealth to Lukoil while coal and steel put Ukrainian Rinat Akhmetov higher up the list than US computer giants such as Michael Dell and Microsoft's Steve Ballmer.
Ten years ago, Johanna Quandt, whose family owned half of BMW, had the nearest claim to being a major manufacturing billionaire: now, thanks to the newcomer nations, the list includes pharmaceutical entrepreneurs, poultry farmers, shipbuilders, chemical refiners and paper-makers.
And the age of the new rich is falling. The average US billionaire is 66 – even after Google co-founder Dustin Mosk-ovitch, at 26, brought the mean down. The UK average is three years lower, but the average Chinese billionaire is just 51 – and most Russians are not even 50. The trend is clear: the world's wealth is moving east, and passing into younger hands. Carlos Slim, at 71, should watch out.
Top 10 Billionaires
1 Carlos Slim, Mexico, telecoms: $74bn
2 Bill Gates, US, Microsoft: $56bn
3 Warren Buffett, US, investor: $50bn
4 Bernard Arnault, France, luxury goods: $41bn
5 Larry Ellison, US, Oracle: $40bn
6 Lakshmi Mittal, India, steel: $31bn
7 Amancio Ortega, Spain, Zara: $31bn
8 Eike Batista, Brazil, mining and oil: $30bn
9 Mukesh Ambani, India, chemicals: $27bn
10 Christy Walton, US, Wal-Mart: $27bn
Compared with 2001
1 Bill Gates, US, Microsoft: $59bn
2 Warren Buffett, US, investor: $32bn
3 Paul Allen, US, Microsoft: $30bn
4 Larry Ellison, US, Oracle: $26bn
5 Theo & Karl Albrecht, Germany, Aldi: $25bn
6 Prince Alwaleed, Saudi Arabia, oil: $20bn
7-11 Walton Family, US, Wal-Mart: $19bn each
12 Johanna Quandt, Germany, BMW: $18bn
13 Steve Ballmer, US, Microsoft: $17bn
14 Kenneth Thomson, Canada, media: $16bn