As a change from regime-changing abroad, President George W Bush, before leaving office soon, may be considering some name-changing at home. Other countries have changed their names in the past – for instance Mesopotamia became Iraq and the USSR is now called Russia. Bush is unlikely to opt for New Iraq, though he might choose Eriksonia or Brendania. But why change the name at all? What's wrong with America?

Americans usually love celebrating the anniversaries and centenaries of important people and events in their country. Last year they had a really major event to commemorate, a quincentenary no less. But it was marked by almost total silence. No parades, exhibitions, speeches, postage stamps, no tributes whatsoever to honour the man after whom America is named, Amerigo (or Henry) Vespucci. The reason, it seems, is because recent historical research on Amerigo, especially by the American historian, Professor Felipe Fernandez-Armesto, who recently published a biography of him in English, Amerigo: the man who gave his name to America, reveals disturbing things about him. It appears he wasn't quite as lily-white a hero as many Americans might like to believe. In fact, he was, says Armesto, a liar and a cheat.

The third child of a lawyer, Nastagio Vespucci and his wife Lisabetta, Amerigo was born in Florence in 1451. He got his early education at St Mark's Dominican school, where his uncle Giorgio was a priest, and later studied astronomy, geometry and physics. His colourful career began when he became manager of the palaces of Lorenzo the Magnificent, then head of the multi-millionaire Medici family, whose name was synonymous with Florence for centuries. They were international businessmen and financiers – popes were among their clients – but some of their "business" and murderous activities make American mafia godfathers look like cherubic choirboys.

Poet and patron of the arts, Lorenzo was also a ruthless political tyrant and schemer who 'arranged' for one of his six children, Giovanni, to be made a cardinal at 14 and, at 37, Pope Leo X. He was described by one papal historian as "a devious and double-tongued politician and an inveterate nepotist." Lorenzo's nephew Giulio, whom he reared, later became Pope Clement VII and patron of Machiavelli and Michelangelo.

Amerigo learned a lot from Lorenzo, who treated him as a friend and soon promoted him in his international financial business. It was shortly after Vespucci was made boss of the Medici operations in Spain – they financed many of the early transatlantic voyages of discovery – that he became an explorer.

Some claim he made four transatlantic voyages, others say even six, but only two can be verified. Two letters attributed to him were published during his lifetime. One, called Mundus Novus (New World), described a voyage to South America in 1501; it was printed and widely distributed throughout Europe. The other, sent to a Piero Soderini, claimed to be an account of four voyages. Some historians have suggested that both letters exaggerated Amerigo's role and made false claims about his travels; others maintain that the two letters were not written by him at all, but were forged.

Amerigo claimed to have sailed down the eastern South American coast as far as the tip of Argentina and to have discovered South Georgia Island near the Antarctic; and also to have cruised up the North American coast as far as the Gulf of St Lawrence, south of Greenland and the Arctic. On his way, it's said he discovered the River Amazon and made a fortune from Caribbean people by trading them trinkets for gold and pearls.

The centuries-long dispute about the number of voyages and the letters regarding them is all quite confusing. But Prof Armesto has no doubt that Amerigo was "a ruthless borrower of others' experiences" and that his accounts of them are "lies, outrageous fantasies and amazing self-reinventions.... Lying, which was habitual with Vespucci, sometimes accompanied other forms of dishonesty."

Some of Amerigo's alleged voyages were made in the service of Spain, others in that of Portugal. He became a Spanish citizen and King Ferdinand made him Spain's Pilot Major or head of the admiralty. In 1505 he married Maria Cerezo, but had no known children. In his fine home in Seville he had seven servants. Unlike Columbus, who was so religious that his canonisation cause was considered in the 19th century, Amerigo seems to have had little time for God. "I hold the things of heaven in low esteem and even came close to denying them," he once admitted. When he died from malaria in 1512 he left his fortune to his wife - and his name to America.

Or rather, this was done by Canon Martin Waldseemüller - a German cartographer and professor at St Dié Academy in Lorraine. In 1507 he published a famous map naming the New World America, though he soon realised the claims he made on Amerigo's behalf were false and, too late, gave the honour, again mistakenly, to Columbus.

Discussing the merits of the other two candidates - Leif Erikson, the Icelandic explorer who landed in North America 500 years before Columbus, and St Brendan, who may have reached there 400 years before Erikson - Prof Armesto seems to favour the Irishman. And Tim Severin, an Englishman, recently proved that Brendan could have been there first. So George Bush's successor might well be the first President of the U.S.B., the United States of Brendania!