Mr Thatcher is a professional international fixer. Ameristar, based in Dallas, is just the latest of his initiatives and already it is embroiled in controversy. A Texan businessman, Jay Laughlin, has accused Mr Thatcher of racketeering and fraud in his takeover of Ameristar.
Mr Laughlin was the largest stockholder until Mr Thatcher allegedly 'hijacked' the firm and bought a majority holding. Mr Laughlin is suing in the Texan courts for dollars 4m.
Mr Thatcher must rank among the most successful businessmen of the 1980s. Some estimate his fortune at more than pounds 40m. Yet before his mother became Prime Minister in 1979 he had little money; by the time she stood down, in 1990, he had a mock Georgian home in Dallas and was shortly to buy a pounds 2.1m mansion in Kensington, south-west London. There have been allegations, but never proof, of mother and son working together to win overseas contracts. In 1984, the Observer published details of Mr Thatcher's involvement as a consultant for the British company Cementation, which was trying to build a university in Oman. Mrs Thatcher went to Oman to lobby on Cementation's behalf for the pounds 300m contract. The following day her son arrived in the country with no one aware at the time that he was acting as the firm's consultant.
In November 1992, as parliamentary concern over Mr Thatcher's business interests grew, in the wake of the Al- Yamamah deal, Ken Livingstone, Labour MP for Brent East, told the House of Commons of claims that Mr Thatcher had acted as a fixer on the 'Supergun' project.
According to Mr Livingstone, a South African human rights activist alleged that Mr Thatcher was promoting the sale of South African heavy artillery to Saudi Arabia. Britain, at the time, had an arms embargo on South Africa. It was also claimed that he had offered to act as the 'middleman' for the South African state arms manufacturer, Armscor, in a deal said to be worth more than pounds 300m.
Mr Livingstone also alleged in the Commons that Mr Thatcher was a friend of Carlos Cardoen, a Chilean arms manufacturer responsible for supplying Saddam Hussein with a variety of military equipment including chemical weapons technology.
Last year, Mr Thatcher left his base in Lausanne, Switzerland, where he was technically a resident, after the government and the justice department started to investigate his arms-dealing activities to see whether they breached residence rules. Neither investigation produced any evidence.
To those who knew him in the early days, Mr Thatcher's involvement in the sometimes seedy and murky world of high finance arms dealing comes as a surprise. The young Mark was a keen tennis and racquets player. While he was at Harrow school, he shone at sport but not at academic work.
He left school at 18 with a few O- levels and possibly (though it has never been accurately confirmed) one A-level. He told friends that he had won a place at Oxford University. But if he did, he passed it up, and headed instead to a job in Hong Kong fixed up by his father. That did not work out and he finally found work with the accountancy firm Touche Ross. But he failed his Part II chartered accountancy exams three times and eventually gave up.
All he really wanted to do was to become a motor racing driver, and when his mother became Prime Minister in 1979 he found plenty of friends willing to fund his obsession. He drove at Le Mans in 1980 and 1981 and crashed both times, and then he got lost in the Sahara during the Paris-Dakar rally. It is a moment mainly remembered because it prompted his mother to cry in public.
Mr Thatcher was quick to recognise the opportunity that his mother's election gave him and set up his own company called Monteagle marketing. It got off to a slow start and he did some modelling to bring in the cash. He received dollars 40,000 advertising tenniswear in the US and dollars 50,000 for promoting whisky in Japan.
In 1984, he left for Texas, with a pounds 45,000 deal to promote the interests of Lotus and British Car Auctions in the US. In 1987, he married Diane Burgdorf and it was around this time that he finally made his fortune.
One source close to Mr Thatcher said that his parents had always worried about him, and he always wanted to prove to them that he could succeed. 'This was the classic case of a son who is favoured by his mother but doesn't have the ability or skill to meet her expectations. But he can work hard. Still, he is insecure, so desperate to make his mum proud of him, and he became brash and arrogant as a result.'
Around 1987, he received a large sum, perhaps as much as pounds 12m, for helping with the Al-Yamamah deal. His mother played an instrumental role in pressing the Saudis to give the contract to British defence firms.
He had been in training for Al- Yamamah for some time. He had made many friends in the arms business and had allegedly been involved on the periphery of some deals during the early 1980s. His best and most useful friend was Wafic Said, who gave him a Rolex watch and played a critical role in the negotiations for Al-Yamamah.
In Dallas, people knew Mr Thatcher because of his involvement in a burglar alarm company called Emergency Networks. He has said that he made dollars 6m from his investment in this firm. Some say he put up dollars 100,000; others dollars 2m. Local businessman have told reporters that the notion that the company in question could generate anything like dollars 6m is 'ridiculous'. Two years ago, Lady Thatcher turned up in Dallas and was interviewed on the local television station. The programme was sponsored by Emergency Networks.
His mother has never been able to accept criticism of his activities and has chided the media for prying into private lives of her family.
Mr Thatcher's businesses appear to have encountered difficulties and some say that his trip to Baku may reflect his concern at the prospects for Ameristar. In June, it filed for bankruptcy in a US court to protect itself against creditors. It owes pounds 12m to suppliers, including Shell and Mobil.
David Wallace, a Texan entrepreneur, is the man who runs Ameristar for Mr Thatcher. Mr Wallace was until recently also treasurer of Lady Thatcher's foundation in the US.
Mr Thatcher has played a key role in fundraising for the foundation. Businessmen in Hong Kong were said to have been horrified when he told them it was 'time to pay up for Mumsie'.
Mr Thatcher very rarely responds publicly to his critics. The last recorded comment was in 1993 when, in response to continuing parliamentary accusations, he said: 'They have nothing on me. This is the thanks I get for being a good British businessman.'
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