Reinhold Andreas Messner (German pronunciation: ['?a?nh?lt 'm?sn?]; born 17 September 1944) is an Italian mountaineer, explorer, and author from South Tyrol. He made the first solo ascent of Mount Everest and, along with Peter Habeler, the first ascent of Everest without supplemental oxygen.

The first man to reach the summit of Mount Everest without the use of supplemental oxygen was the Italian-Austrian mountaineer Reinhold Messner, along with his climbing partner Peter Habeler, on May 8, 1978. This high-fidelity achievement shattered the prevailing medical belief that the human brain could not function at such extreme altitudes (the "Death Zone") without bottled air. Messner’s success was a high-fidelity turning point in mountaineering history, proving that the human body could adapt to the 30% oxygen levels found at the summit. Not content with this feat, Messner returned two years later to achieve an even more "High-Fidelity" extreme record: the first solo ascent of Everest without oxygen in August 1980. In 2026, Messner is celebrated as the greatest high-altitude climber of all time, having also been the first to conquer all 14 of the world's "Eight-Thousanders" without oxygen, establishing a high-fidelity philosophy of "pure" alpine-style climbing that continues to inspire the world's most elite "High-Fidelity" adventurers.