Mike Horn made his name by walking to some of the world's remotest spots but as the Dakar Rally resumes on Sunday, he is in a diesel car, trying to navigate the Saudi Arabian desert with the aim of "conserving the planet".
Horn, a 54-year-old Swiss based South African, is famed for exploits that include circling the Equator without using any motorised transport and walking to the North Pole in winter without dogs or motor vehicles.
He is competing in his second Dakar Rally, as navigator for veteran French driver Cyril Despres, in a traditional diesel-powered car with the objective of making such cars obsolete.
In addition to competing, the car is designed to collect data as part of a project named Gen-Z which aims to enter a competitive hydrogen-powered car in the 2023 rally.
The car has been fitted with sensors by the French Alternative Energies and Atomic Energy Commission (CEA) which plans to manufacture the prototype that will run on an electric motor powered by a hydrogen fuel cell.
"There's a real goal behind all this, and it's essential," said the 46-year-old Despres, who is in his 21st Dakar rally and has won the motorbike category five times. "That's new for me."
Horn first raced last year, when he and Despres lasted three stages. The explorer took heavy criticism for participating in a rally with a notorious carbon footprint.
"There are three things that made me come back," he said: "First of all the human adventure, then the competition, I like to win and to reach the end of my expeditions and of course collect data for research and for future generations."
"I can play an important part in changing the way we participate in motor sports," said Horn.
"To conserve the planet to be able to leave a future to the younger generation is one of my life missions."
After a rest day on Saturday, the rally resumes Sunday with the 737 kilometre seventh stage and Frenchman Stephane Peterhansel leading in the car class.
With 55 cars still running and six of the 12 stages remaining, Horn and Despres are 17th in their 340 horsepower Peugeot, 3 hours 42 minutes and 59 seconds behind Peterhansel.
Despres said it was important to compete.
"If we drive at 50% of the speed required to be with the best, the CEA will not be able to make a fuel cell with the power needed to win. We have to push as hard as we can to make this data real," he said.
For the moment, their biggest problem is navigation.
"Last year we were only able to do three stages," said Horn.
"I couldn't learn navigation with the roadbook in only three stages. Besides I have to do it in French, it would be easier for me to do it in Afrikaans."
He said that navigating in a rally field was different from crossing remote regions alone on foot.
"When you walk where no one has ever walked before it's different from when you have 40 cars in front of you," he said. "I have to be able to look up from the roadbook to look outside, find the sun or a line of dunes to find my way around."
They are accompanied in Saudi Arabia by Matthieu Parent of Vaison Sport, a French company that specialises in building prototype race cars.
"We need to create a new vehicle around the fuel cell," Parent said.
"To manufacture a vehicle that emits only water vapour and capable of winning the Dakar in 2023 is tough, but it is possible."