Mr Tompkins, now 54, decided to sell off most of his holdings - for an estimated $125m - and dedicate himself to protecting the environment. But not everyone trusts his motives.
In Chile, where Mr Tompkins has bought up some 1,100 square miles of spectacular land with a view to creating the world's biggest privately- owned nature reserve, he has been accused of everything from being a US agent to letting Israeli soldiers train on his land, from trying to divide Chile into two nations to planning to turn the region into a nuclear waste dump.
He insists he is simply a "generous philanthropist" who wants to protect virgin forests from loggers, and plans to hand the area to a Chilean foundation once he has turned it into a reserve with facilities for eco-tourists, hikers and outdoor sport lovers.
Essentially, the former clothing magnate has run into Chilean suspicion of foreigners, particularly Americans. Chileans have always been considered the most xenophobic of South Americans, but Mr Tompkins has also split the nation along the lines of its recent history. While liberals support him, the still-powerful right-wing supporters of the armed forces chief, General Augusto Pinochet, and their allies in the business community have joined the criticism, fearing he is becoming a figurehead of a growing ecological movement they see as a threat to traditional forestry and mining interests.
Military officers say Mr Tompkins should never have been allowed to buy up territory which effectively cuts Chile in two at its narrowest point, between the towns of Puerto Montt and Chaiten, and is vital to national security because it runs up to the border with Argentina. They note that he also has land on the Argentine side, though not continguous with his Chilean property, which he has promised to hand over to Argentina as part of a national park.
Mr Tompkins says he has received death threats and his phones have been tapped as part of "a campaign of accusations and harassment". His lawyers leave no doubt he is blaming the military and some members of the government of President Eduardo Frei.
He also complains that his picturesque log-cabin home at Renihue has been buzzed by Chilean air force planes and helicopters. "They fly at high speed, sometimes as low as 100ft, frightening the kids in the local school for children of our workers," he said.
"This is our national territory and airspace, not Tompkins's territory," retorted Belisario Velasco, Chile's deputy interior minister and the leading opponent of the project. "The government is not harassing him. It is only making sure the laws are obeyed."
The Defence Minister, Edmundo Perez, has called the American "arrogant, irritating and out of place", and even Mr Tompkins's supporters admit the minister has a point. The self-styled philanthropist has become increasingly abrasive as the obstacles mount. "Frankly, it's frustrating that we're spending half our time, money and energy defending the project instead of getting on with it," he said last weekend, after flying three MPs over the land in his own aircraft.
Mr Tompkins has tried to win over Chile's youth, giving lectures and slide shows almost daily in universities and colleges, saying the destruction of virgin forests by loggers or families seeking firewood was what first attracted his attention. One of the questions he is most often asked is: how much did you pay for the land? "I don't know," he replies, not altogether convincingly for a former multinational businessmen. "I bought it bit by bit, mostly from other foreigners, Swiss, Italians ... the price per acre varied."
The area has been open to the public since 1995, but Mr Tompkins estimates it will take up to eight more years to get the park in full swing. To criticism that he is only in it for profit, he insists he will hand it over to a Chilean foundation "whenever we feel a Chilean foundation is able to take over". But the torrent of criticism he has unleashed may take the timing out of his hands.