Bill Gates takes the stage at Live 8

Microsoft founder and chairman Bill Gates made a surprise appearance at the Live 8 concert in London's Hyde Park today to urge world leaders to do more to ease the problem of Africa's crippling debt and extreme poverty.

Gates' presence on a stage shared with the likes of Elton John, REM and Coldplay may have seemed out of place to some but he was also in the presence of famous friends and fellow humanitarians such as U2 singer Bono.

Gates was introduced to the crowd by Live 8 founder Bob Geldof who praised the charitable work of the Bill & Melinda Gates foundation and hailed the software tycoon as the world's most important philanthropist.

Gates told the crowd and a worldwide audience of millions "if you show people the problems and you show people the solutions they will be moved to act".

"The huge turnout for Live 8 here and around the world shows that," he added.

Gates said, if successful Live 8 will prove to be the "best thing humanity has ever done".

For many, Gates' final task of introducing UK singer Dido will have served as evidence of the slightly surreal nature of such all-star, cross-cultural events.

World's richest man delighted to introduce Dido.

However, a number of the musicians and comedians taking part in the BBC's broadcast coverage of the live event also made the softly spoken and understated Gates a butt of some fairly predictable jokes.

Comedians David Walliams and Matt Lucas, who had previously introduced Elton John, made light of Gates' stage presence and his failure to work the crowd like some of the other acts on the bill, while host Jonathan Ross questioned why the Microsoft boss hadn't stuck around to "explain why Windows keeps crashing".