Klaus Märtens was a doctor in the German army during World War II. While on leave in 1945, he injured his ankle while skiing in the Bavarian Alps. He found that his standard-issue army boots were too uncomfortable on his injured foot. While recuperating, he designed improvements to the boots, with soft leather and air-padded soles made of tyres. When the war ended and some Germans looted valuables from their own cities, Märtens took leather from a cobbler's shop. With that leather he made himself a pair of boots with air-cushioned soles.