In 1492, Vespucci was sent to Cadiz by his employer to investigate corrupt practices within the Medici's Spanish operations. While he was there, he became involved in the fitting out and provisioning of vessels bound for the Indies. He may actually have provided beef for Columbus's voyages at this time. Soon afterwards, Vespucci was invited by the King of Portugal, Manuel I, to particate in a series of voyages down the eastern coast of what is now known as South America. Up until this point, Christopher Columbus had always maintained that the 'New World' was the eastern side of the continent of Asia. It was the idea that this new landmass was actually a separate continent that led it to be named after Vespucci rather than Columbus.
However, it was not the voyages themselves that led to Vespucci's fame. It was a series of letters written over this period that were widely published in Europe and which awakened the public to the various discoveries of the New World. They also led to a new world map being created by cartographer, Martin Waldseemüller, where the new continent was given the name 'America' for the first time.
There was some dispute over the number of voyages that Vespucci made, and indeed over the authenticity of the letters that were published, with many claiming that Vespucci was trying to undermine Columbus's achievements. However, discoveries of genuine letters in the 18th century indicated that the published letters may well have been fabrications by others, based on the genuine letters written by Vespucci.
Vespucci became a Spanish citizen soon after his return to Spain. In 1508, Vespucci was made 'Chief of Navigation' for Spain and asked to found a 'School of Navigation' by King Ferdinand, keen to develop the navigational techniques used by Spanish sea captains exploring the world. Vespucci was responsible for developing a rudimentary, but fairly accurate, method of calculating longditude, essential for navigating across oceans. This technique was only improved upon much later. He died on February 22, 1512 at his home in Seville, Spain.