The Gates foundation, which is worth $30 billion, (£17billion), is now the largest charity to have been created by a single benefactor or private company by a factor of three, following a previous $3 billion gift from its founder last July. Mr Gates has stated that he intends to give away 90 per cent of his fortune, which is currently valued at about $50 billion.

The causes to which he has channelled his wealth — global health inequalities, education programmes, public libraries and projects around his home town of Seattle — have changed dramatically because of his contributions.

To date, the Global Alliance for Vaccines and Immunisation has been the largest recipient of his charity. His pledge today follows an initial $750 million grant in 1999, which was used to help to set up the organisation to support research and improve access to vaccines.

As well as saving an estimated 670,000 lives through vaccines, it has also helped to facilitate major breakthroughs on vaccines for diseases such as malaria, rotavirus and meningitis.

Other grants given by the foundation, which hands out $1.1 billion of funding a year, include $1 billion in 1999 to the United Negro College Fund to pay for scholarships.

Mr Gates’s donations, which far surpass even the philanthropy of Andrew Carnegie and John D. Rockefeller, dwarf the next largest such charitable foundations.

The Lilly Endowment, created by the drugs giant Eli Lilly and Company in 1937 to support religious, educational and community development, is currently valued at $10 billion. The Ford Foundation, created with gifts by the motor magnate Henry Ford in 1936, is the third largest at $9 billion.

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