Elon Musk, the billionaire owner of SpaceX and Tesla Motors, has a plan to stop computers from taking over the world. The co-founder of Paypal - who made his first fortune in his twenties - has joined other tech giants to fund a not-for-profit company called OpenAI. Its aim is to develop the most advanced forms of artificial intelligence and then to share the results. Musk is among a group of thinkers - including Stephen Hawking - who have warned that AI could eventually lead to the end of the human race. His idea is that by making AI 'open source', powerful corporate interests will be kept in check. Mark Coles explores the life of a man with a passion for rockets, cars and a plan to retire to Mars.

Producers: Smita Patel and Sally Abrahams.