When did the first successful climb of Mount Everest without supplemental oxygen happen?

The first successful ascent of Mount Everest without supplemental oxygen was achieved on 8 May 1978. Reinhold Messner of Italy and Peter Habeler of Austria reached the summit using only their own physical capacity in the extreme thin air. At 8,849 meters, Everest’s summit has only about one-third the oxygen available at sea level. Their climb challenged long-held beliefs about the limits of human physiology. It became one of the most important feats in high-altitude mountaineering.