Bill Gates, the world's richest man, yesterday emerged as the most philanthropic person on the planet after donating another $5bn to his charitable foundation.

The latest gift by the founder of Microsoft, the software giant, brings the total managed by the Bill and Melinda Gates Foundation to $21.8bn (£13.2bn) - edging it past the UK's Wellcome Trust, which has assets of £13.0bn.

Yesterday's announcement coincides with the latest development in the long-running legal battle between Microsoft and the US justice department, which has accused the company of abusing its monopoly position in the world's software market.

Mr Gates and his wife have appeared to become far more generous since the US government's anti-monopolies case started in 1998.

Last year Mr Gates said he was committed to giving away the majority of his wealth, estimated at about $100bn and based on his 15% stake in Microsoft. The foundation has focused on health and education issues around the world including work to limit the spread of Aids in Africa.

Three months ago the foundation announced that it would donate $750m over five years to help vaccinate children in developing countries. To keep its tax-exempt status the fund must give away at least 5% of its endowment each year.

Government officials were yesterday preparing to present their rebuttal of Microsoft's defence in Washington. The response is expected to argue that the company has ignored the indictment of its behaviour already made by the trial judge, Thomas Penfield Jackson.

Bad weather on the east coast of the US was yesterday threatening to prevent the government from physically filing its 30-page rebuttal to a snowbound courthouse.