Bill Gates is one of the world's best-known billionaires - but after years at the corporate coalface building a software empire and a vast fortune, his priority now is giving that wealth away. And his ethos for doing it has been shaped by science.

Famed for co-founding Microsoft, in recent decades Bill’s attention has turned to philanthropy via The Gates Foundation: one of the largest charities in the world. Since its inception in 2000, the organisation has helped tackle issues around health, education, inequality and climate change in some of the world’s poorest countries, with an undeniable impact, from contributing to the eradication of wild poliovirus in Africa, to helping halve global child mortality rates within 25 years.

But, as Jim al-Khalili discovers, for a man with lofty ambitions and an even loftier bank balance Bill has surprisingly humble tastes.