Stanley Fink's world changed in late 2004. The chief executive of the Man Group, one of Britain's highest-paid businessmen, was on safari in Botswana with his wife, Barbara, daughter Gabriella and sons Jordan and Alexander when he was struck dumb in mid-sentence.

Terrified, he wondered whether he had been attacked by a virus or was in the throes of a nightmare. After 40 minutes, he regained the power of speech, gathered his family and caught a flight to South Africa for medical help.

Doctors there told Mr Fink, now 48, that he had suffered a minor stroke. But back in London it was discovered he had a colloid cyst, a benign brain tumour the size of a poached egg.

He had an operation to remove it that September. Three months later, he was back in the driving seat in Man's glass-fronted offices in Sugar Quay, the site of an old commodities landing stage on the bank of the Thames, next door to the Tower of London.

Medics had asked Mr Fink whether he wanted to retire. He did not, but the scare had made him reassess his life and priorities. Yesterday, Mr Fink became the latest in a string of high-flying businessmen to step down to devote more time to charitable works. He follows a path well trodden by the likes of the UK mobile phone entrepreneur John Caudwell, the HSBC investment banker John Studzinski, and the American billionaires Bill Gates and Warren Buffet.

Over two decades at Man, Mr Fink has amassed an estimated £180m personal fortune orchestrating lucrative investments for companies and the super-rich. Last year alone, Mr Fink pocketed £6.5m in cash and bonus. Under his stewardship, Man has ascended to the pinnacle of the controversial hedge-fund industry, whose inexorable rise has been one of the key trends in global finance in the past decade.

Hedge funds are unashamed money-making machines, enormous reservoirs of cash that take bets on any market, anywhere, from shares to oil to currencies. For those who invest, the returns can be eye-watering. So too can the rewards for those managing the money. Man enjoys a reputation as the creator of one of the largest bands of millionaires in London.

Harvey McGrath, the Belfast-born chairman of the group and another renowned philanthropist, is worth an estimated £120m. He is a trustee of New Philanthropy Capital, a charity that advises the rich on how best to give away their wealth, and Charity Technology Trust, which advises charities on the best use of technology.

Mr Fink took home £11.7m in cash and bonuses in three years and has homes in north London, France and Spain. He owns hotels, including the opulent Hotel Kilimanjaro in the upmarket French ski resort of Courchevel, and a private construction company that builds villas in the Alps.

Mr Fink is also a leading light of a tight-knit community of publicity-shy, fabulously wealthy, City philanthropists who mingles business with show business, royalty and the arts. During his tenure, Man became a regular backer of exhibitions at the Royal Academy and the lead sponsor of the Booker literature prize, now known as the Man Booker Prize.

The company's boardroom is lined with first editions of long- and short-listed Man Booker contenders and other titles by those authors, which staff are free to borrow. Winners of the prestigious prize need not apply to Man to manage their £50,000 windfall. Clients typically invest about £100,000 in two or three of its funds.

Mr Fink chaired the fund-raising committee of the Evelina's Children's Hospital, part of London's St Thomas's Hospital, working with the Princess Royal raise £10m, much of it from the hedge-fund industry, to move the department to a new state-of-the-art site in Lambeth Palace Road. The Sunday Times Giving List, which tracks philanthropy in Britain, ranked Mr Fink ninth last year. He was also rated the country's 511th wealthiest individual by the newspaper.

He is an enthusiastic fund-raiser for Burlington Danes Academy, a school in Fulham, and is a trustee and generous donor to Ark children's charity.

Organised by Arpad Busson, a fellow-trader and the former partner of the Australian supermodel turned lingerie entrepreneur Elle "The Body" McPherson, Ark, or Absolute Return for Kids, is a hedge fund for children and one of the country's fastest-growing charities.

Despite their shared dedication to charitable works, the styles and sensibilities of Mssrs Busson and Fink could not appear further apart. Mr Busson, a Swiss-born, London-based financier, divides his time between offices scattered around the globe, his villa in the Bahamas and his mansion in Notting Hill.

The Riviera playboy and gossip column favourite counts Hugh Grant and Jemima Khan as close friends, and Madonna and Guy Richie as associates.

In sharp contrast, Mr Fink evinces an evident discomfort at ostentatious displays of wealth, perhaps derived from his no-nonsense northern roots.

He told The Independent: "For me, I was brought up in a poor home but my parents would give if there was a good cause. How much you give is a function of your wealth. Was it £10 or £50? Now it's £1,000 or £100,000. I do it from wanting to help from common humanity and caring about fellow human beings. I give to human charities and not animal charities. There is a choice.

"In terms of guilt, I've never done anything in my working life that I can't face myself in the mirror about. If I've treated myself to something new or an expensive holiday, the fact that I've donated a similar amount to charity in the previous week or year makes you feel you're not only being self-centred or selfish.

"There's no doubt it gives you a comfort. It means that when I spoil myself it makes it a bit more seemly and less embarrassing on your conscience. Charity does fulfil that purpose. I don't do it out of guilt. I do it because it needs to be done."

Born in the Crumpsall area of Manchester, his father made lampshades before running a grocery corner shop. The young Stanley, a life-long Manchester United fan, was reportedly driven by a desire to escape lower middle class financial insecurity.

"My father was not in any way a negative role model, but I looked around at him and his generation of middle managers," Mr Fink said. "It made me shape my career to try never to end up like that, as an unsuccessful middle manager living near the edge."

He won a place at Trinity Hall, Cambridge, where he read law and met his wife. He was awarded a second-class degree and, to his surprise, struggled to secure a job with a law firm. Instead, he joined the accountancy firm Arthur Andersen, where he worked until 1982. From there, he moved to the financial planning department of the confectionery group Mars but soon shifted to the buyout team at Citigroup, the world's biggest financial group. ED&F Man, then predominantly trading in commodities, was a client.

A deal with a Man subsidiary failed to happen, but the company - set up in 1738 by barrel-makers Edward Desborough and James Man, who supplied rum to the Royal Navy - liked Mr Fink and invited him to join.

He took up the offer in 1987 and began Man's transformation, joining the board aged 29 and becoming finance director five years later. After 200 years as a partnership, he spearheaded the company's flotation on the London Stock Exchange 1994. Two years later, he became managing director of the company's asset management arm, Man Investments, later buying AHL, a small hedge fund.

During this time, he worked in Switzerland to be close to more wealthy individuals. A curious, but untrue, story often told was that Mr Fink swam to work across Lake Zurich each morning. In an attempt to enact the myth, and raise money for charity, he made the swim two years ago.

In 2000, the group split, and Mr Fink took the helm of Man Group. By that time, Man managed $4.7bn. Now it invests $54.7bn on behalf of pension funds, big City institutions and the very rich.

The hedge-fund industry has yet to shed its reputation as the bogeyman of the financial world, a reputation it first earned with the legendary attack on the Bank of England in 1992 by the speculator George Soros that forced Britain out of the exchange rate mechanism and cost taxpayers £4bn. Black Wednesday is still known in Mr Soros' firm as White Wednesday.

In 1998, the hedge fund world was dealt a further public relations disaster by the collapse of America's Long Term Capital Management, run by a pair of Nobel Prize-winning economists.

Mr Fink has done more than anyone to rehabilitate and build the reputation of his industry and those who work in it. Now he hopes to be remembered not just as the man who made hedge funds respectable, but as one of the UK's greatest philanthropists.

The great givers

Bill Gates

The world's richest man has said that he plans to move to a part-time role in his company Microsoft by 2008, to devote more time to philanthropy. The Bill and Melinda Gates Foundation is the world's biggest charity, with an endowment of $60bn (£32bn). It combats tuberculosis, malaria and HIV and Aids. Born in Seattle in 1955, Mr Gates is the youngest of the great philanthropists.

Warren Buffet

The death of his wife in 2004 prompted Mr Buffet, considered one of the greatest stock market investors of all time, to donate $30bn (£16bn) to the Bill and Melinda Gates Foundation. Born in Nebraska in 1930, Buffet ran his first business in his bedroom. Despite his colossal wealth, the head of US investment firm Berkshire Hathaway is known for leading a simple lifestyle.

Andrew Carnegie

The Scots-born US steel tycoon Andrew Carnegie said: "The man who dies leaving behind him millions of wealth will pass away unwept, unhonoured and unsung." Born to a family of poor mill workers in 1835, he emigrated to the US. Before he died in 1919, Carnegie gave away $360m (equivalent to £4.4bn today). He built libraries, schools and universities.

Lord Sainsbury

Following in the family tradition of charitable giving, Lord David Sainsbury founded the Gatsby Charity Trust in 1967. He believes that philanthropic giving is not just about signing cheques, but requires a commitment of time and effort. In 1993, the former chairman of the Sainsbury's Group and Labour life peergave more than £300m to the Gatsby Charity Trust; the largest charitable gift ever recorded in Britain.

John Studzinski

The joint-head of HSBC's investment banking division gives half his annual salary to human rights causes, the homeless and the arts. In 1996, the Polish-American banker set up the Genesis Foundation to support young artists, playwrights and musicians. He is the chairman of Business Action on Homelessness and co-founded the Passage Day Centre, one of London's largest centres for the homeless.

John Caudwell

The Mobile Phone King was last year ranked 29th in The Sunday Times Rich List, which estimated his fortune at £1.28bn. Last month he sold the Caudwell Group, which includes the high street chain Phones 4u. He now devotes his time to the Caudwell Charity, founded in March 2000. A firm believer in "philanthropy through capitalism", he has cycled all over the country to raise money.

Franziska Wetzel