Discover the inspirational story behind Salman Khan's free online tutorials that are already watched by millions, including Bill Gates's children. His aim is to create the first free, world-class virtual school.

Khan Academy: The man who wants to teach the world

Nadia passed her retake with flying colours, and soon many more relations and friends wanted Khan's help. Unable to handle the volume of requests, at the suggestion of a friend he started to record his lessons on video and post them on YouTube. 'At first I was dismissive,' Khan says.