At midnight on May 21, Kilian Jornet stood on top of the world. He carried neither oxygen cylinders nor ropes, and no guides or Sherpas were at his side. The 29-year-old was alone, light and nimble – the torch beams of expensively assembled expeditions on the mountain far below punctuated the blackness. With his lightweight kit, a few energy gels and just a single litre of water, he looked more runner than mountaineer. Which, of course, is precisely what he is: the greatest mountain runner in history, in fact.

Seemingly not constrained by the same laws of physics as the rest of us, the Catalan mountain goat had just set a record for the fastest known time (FKT) ascending the planet’s most fabled peak: a scarcely believable 26 hours from base camp on the Tibetan side of Everest to the 8,848m summit. Wearing custom-built shoes engineered by his sponsor Salomon, he’d run the first stretch in the style of one of the mountain trail-running races he’s dominated for nearly a decade, before pulling on crampons and advancing into the more technical terrain. Passing seasoned mountaineers taking up to four days to toil their way up into the ‘death zone’, he’d continued in a single push to the top. Some had scoffed at his aim to ‘run up’ Everest. But, by any relative measure, this was exactly what he had achieved.

‘From the top, I could make out the neighbouring mountains, Cho La and Lhotse, the plateaus. It was truly beautiful,’ says Jornet, typically more concerned with the value of the experience than the scale of his achievement. ‘Everybody can climb how they feel they want to – there’s no good or bad way. But for me, I wanted to see if it was possible to do it in one go, with no oxygen, no ropes, faster. My way: it felt good to be alone up there. To just enjoy the moment and not have to think about other people.’

A Himalayas novice Jornet may have been. But the Alps-based ultra runner knew more than enough about mountains to understand that the summit, as the saying goes, is only halfway. Despite the success of his FKT, the ascent had been far from straightforward – his 5ft 7in, 58kg frame wracked by agonising cramps and vomiting exacerbated by extreme exertion in an environment entirely hostile to even the most physiologically gifted of humans. 

So, at that point, he’d abandoned his plan to descend all the way back down to Base Camp for a neatly bookended time. Instead, he holed up at Advanced Base Camp (ABC), at 6,500m, as the wind picked up. His instincts, as usual, were good; four people died on Everest’s slopes that weekend.

Mountain-running legend Marino Giacometti, pioneer of the high-altitude-trail Skyrunning movement that Jornet has done so much to popularise, followed his protégé’s exploits with both awe and apprehension from his native Italy. ‘This is a great achievement of both endurance and survival,’ says Giacometti. ‘In trail-running terms, this is one of the great performances. No ropes, no oxygen. No one in the world could have done this except Kilian.’

The veteran explorer Sir Ranulph Fiennes, a man not given to issuing breathless praise, particularly not to those who might be seen to be encroaching on his turf, goes even further in assessing Jornet’s talent and achievement: ‘Normal people – and in that I count myself – we have to accept that there are those who can do things which I would say for humans are not possible.’

For Jornet, achieving the impossible in the Himalayas was merely the closing chapter in a five-year odyssey to set FKTs on the world’s most emblematic peaks. The Summits of My Life project began in 2012 with a sub-nine hour ski mountaineering traverse of Mont Blanc (4,801m), in the French Alps. This, Jornet followed with a straight up and down of the Alpine giant from the centre of the mountain sports Mecca, Chamonix. Most mountaineers take two days to scale Mont Blanc, encumbered by heavy kit and complex logistics. Jornet did it in four hours and 57 minutes, wearing a T-shirt, shorts and trail-running shoes, breaking a record that had stood for 23 years in the process and commenting with characteristic understatement that ‘it was a nice experience’.

The 4,478m Matterhorn came in August the following year. Setting off from the elegant white church in the centre of Breuil-Cervinia, and following the classic Lion’s Crest route, Jornet raced up to the woven metal cross that teeters on the summit and back down in the time it takes most of us to log on in the morning, check our emails, have a coffee and consider doing some work: two hours and 52 minutes. The 18-year-old record he broke in the process had belonged to the great Italian mountain runner Bruno Brunod.