Ueli Steck, a Swiss mountain climber nicknamed the "Swiss Machine", died on Sunday after slipping from a slope and falling into a crevasse at around 6,600 meters on Mount Nupste in Nepal, according to CNN.
Steck was 40 years old.
The Swiss climber was acclimatizing himself to try and climb Mount Everest next month without oxygen on a new route. The West Ridge route that he planned on taking has caused more deaths than successful ascents.
Earlier this month, he said that his body was as 'strong as it was never before."
Steck was alone after his climbing partner was unable to make the ascent due to severe frostbite. Steck's body was recovered and taken by helicopter to a hospital, where he was pronounced dead.
Steck previously reached Mount Everest's summit without oxygen in 2012.
Six climbers died on Mount Everest in 2016.