The billionaire financier and philanthropist George Soros was yesterday found guilty of insider dealing by a French court and fined €2.2m (£1.4m).
Mr Soros, whose speculative attacks on sterling in 1992 brought him international fame as "the man who broke the pound", vowed to appeal against the court's surprise decision.
Two other men who were tried alongside 72-year-old Mr Soros, Jean-Charles Naouri, a former top French civil servant, and the Lebanese businessman Samir Traboulsi, were acquitted.
In a statement issued in New York, Mr Soros said he was "astounded and dismayed" by the ruling, which related to a failed bid for French bank Société Générale in 1988.
"I will appeal the decision to the highest level necessary. Let me repeat now what I have maintained form the start: at no point was I in possession of inside information regarding Société Générale. The charges against me are unfounded and without merit."
Lawyers for Mr Soros had earlier argued that the case, which took 14 years to come to trial and involved gathering evidence from Britain, Luxembourg and Switzerland, was too old to judge.
Prosecutors had urged the court to fine Mr Soros - in theory he could have faced jail under French law covering insider dealing but such a sanction is rare.
The €2.2m fine matches the amount of money the prosecution alleged Mr Soros made out of trading in the shares of the Société Générale in 1988 - a year after its privatisation. The French authorities began their investigation in 1989 and Mr Soros was placed on notice that he was under scrutiny in 1993.
The court ruled yesterday that Mr Soros had used inside knowledge about a takeover bid for Société Générale to buy shares in the bank. When the offer subsequently emerged the bank's shares jumped sharply higher.
In his evidence to the court last month Mr Soros said the bid, which failed for lack of support, was common knowledge in French financial markets and he had not obtained any confidential information.
He said he had bought Société Générale shares because he believed the bid would free the bank from political control.
But he said subsequent meetings in Paris had persuaded him otherwise and that he had then sold the Société Générale stake - bought as part of a £50m package that included holdings in other banks - at a huge profit.
At an appearance in court in November he said: "I have been in business all my life, and I think I know what is insider trading and what isn't."
Mr Soros, who was born in Budapest but moved to the US in 1956, is the 37th richest man in the world, according to Forbes magazine, with fortune estimated at $6.9bn.
In 1992 his Quantum Fund made an estimated £1bn by selling the pound heavily on the foreign exchanges. That contributed to forcing the UK government to take the currency out of the exchange rate mechanism, fatally undermining the Major administration's reputation for economic management. More recently the Quantum Fund suffered heavy losses with the collapse of the dotcom boom.
Though Mr Soros established his reputation as a formidable figure in the world's cutthroat financial markets - he is reputed to have been the first American to earn $1bn in a single year - he has used part of his fortune to fund a network of foundations to tackle the problems caused by what he sees as the failures of global capitalism.
In his book Open Society he wrote: "The main failing of global capitalism is that it is too one-sided: it puts too much emphasis on the pursuit of profit and economic success and neglects social and political considerations."