Swiss climber Ueli Steck, one of the most feted mountaineers of his generation and famed for his speed ascents of iconic Alpine routes, died on Mount Everest on Sunday, officials said.
"Today morning, he had an accident on the Nuptse wall and died. It seems he slipped," Ang Tsering Sherpa, head of the Nepal Mountaineering Association, told AFP.
Steck, 40, was on Everest to acclimatise before attempting in May to summit the world's tallest peak followed by neighbouring Lhotse, connecting a series of ridges to design a never before climbed route.
Everest and neighbouring peak Nuptse share a common ridge, which is where Steck slipped and fell, according to a government official.
"He skidded off about 1,000 metres from (Mt Nuptse) camp two early morning on Sunday. Other climbers ascending Everest saw him and asked for his rescue," said Dinesh Bhattarai, director general at the Department of Tourism.
Steck was climbing alone when he died. His partner, Tenji Sherpa, had sustained severe frostbite earlier and was recovering at a lower camp.
His body was recovered by Nepali guides and flown by helicopter to Kathmandu.
The accomplished alpinist sought to pioneer new routes throughout his career, earning the nickname "the Swiss Machine" for his record solo ascents in the Alps.
He was attempting to achieve another first this year by charting a rarely climbed route to summit both Everest and Lhotse, the world's fourth highest mountain, all without the use of supplemental oxygen.
Steck was due to summit Everest via the West Ridge -- a route that has recorded more fatalities than summits -- before climbing Lhotse.
In a video recorded in early April and posted on YouTube, Steck said he would judge the attempt a success regardless of whether he reached the top -- as long as he returned alive.
Mingma Sherpa, the first Nepali to summit all 14 of the world's peaks above 8,000 metres, said the accident -- the first fatality of this year's spring climbing season on Everest -- underscored the unpredictability of mountaineering.
"It is very sad news, he is a very experienced climber," he said of Steck's death.
"Things can be so unpredictable in the mountains and it can be challenging even for the most seasoned climbers."
Tributes poured in for Steck on social media, with British climber Kenton Cool -- who has scaled Everest 12 times -- describing him as "a true inspiration to all".
"A man that showed us all what was possible in the mountains and beyond," Cool tweeted.
- Stalked by controversy -
Steck made global headlines in 2013 when he and two other Western climbers came to blows with a group of furious Nepali guides on Everest.
The brawl shocked the mountaineering community, causing a damaging rift between Western climbers and the often lowly-paid Nepali guides who are essential for commercial expeditions to the crowded summit.
An angry Steck swore never to return to Everest, telling a Swiss website that his "trust (was) gone".
But he was back in the Himalayas only months later, this time to scale Mount Annapurna, the world's tenth highest peak, via its steep Southface wall, becoming the first mountaineer to complete a solo ascent of the 8,091-metre (26,545-foot) peak.
Controversially, he offered no photographic proof of his accomplishment, saying an avalanche knocked his camera out of his hand.
Nevertheless, he was awarded the Piolet d'Or, mountaineering's top accolade, for the 2013 climb.
Born in the town of Langnau im Emmental near the Swiss capital Bern in October 1976, Steck was a devoted climber by the age of 12.
As an 18-year-old, he climbed Mont Blanc's Eiger massif, an achievement that attracted attention and later sponsors, setting him on a course to become a professional climber.
He soon became one of the most prominent names in mountaineering after scaling some of the world's most daunting peaks, often alone and without basic safety equipment such as fixed ropes or bottled oxygen.
But, in an interview with AFP nearly two years before his death, Steck said he was never inspired by a quest for fame or records.
"Personal pleasure alone dictates my approach," he said.
He told AFP that he never wanted climbing to become a "business" and was content when his income exceeded what he previously made as a carpenter.
Steck was however attacked by some in the mountaineering world for resisting the use of GPS to track his movements or refusing to record photographic evidence of his achievements, criticism that he dismissed as "jealousy".