This business is a bit like a drug. When you are doing well, it's hard to quit

Stanley Druckenmiller, Quantum strategist

Mr Soros runs several private investment funds which manage money for wealthy clients.

In April, many of these funds, which make huge bets with borrowed money, are said to have lost more than $5bn after American technology shares lost value.

Mr Soros's flagship $8.5bn hedge fund, Quantum, the world's largest, has now been relaunched as the Quantum Endowment Fund.

Nasdaq plummets

Two of the company's top investment strategists, Stanley Druckenmiller and Nicholas Roditi, are leaving in the wake of the loses.

"I screwed up. I should have got out [of the Nasdaq] market in February," said Mr Druckenmiller, who ran the fund for the past 12 years.

The Nasdaq composite index is down around 25% from its all-time peak of 5,048.62 hit on 10 March.

"I never thought the Nasdaq would drop 35% in 15 days," Mr Druckenmiller said.

Bailing out

"This business is a bit like a drug. When you are doing well, it's hard to quit."

The Quantum Fund yielded average annual returns in excess of 30% during its 31-year history, making Mr Soros and Mr Druckenmiller among the most revered financial gurus.

The Hungarian-born Mr Soros became famous when his fund "bet" millions that the UK would be forced to devalue the pound in 1992.

He won his bet, made lots of money and became known as the "man who broke the pound."

Mr Soros's decision to bow out of highly speculative investing comes only weeks after Julian Robertson, one of the most successful investors, closed down his Tiger hedge fund, after his bets misfired that many "old economy" stocks were undervalued.

Mr Robertson said his decision to close his funds was driven by his view that financial markets were now irrational, driven by emotion rather than sober assessments of value.