Hailed as the greatest living explorer, Sir Ranulph Fiennes has pushed his mind and body to its utmost limits in some of the most inhospitable environments on Earth. Born in Berkshire, his father was a commander in the British Army – a war hero who died just months before he was born. He was brought up in South Africa before being sent to Eton College. Now aged 72, he lives on the edge of Exmoor with his wife and daughter, and continues to take on extraordinary challenges and expeditions – such as the gruelling Marathon des Sables – raising money for Marie Curie and the British Heart Foundation. Interview by Fiona McGowan.