The first man to summit (reach the top) of Mt. Everest was Sir Edmund Hillary in 1953. He was later knighted by the British crown for his efforts. But Hillary was a New Zealander. The first documented Brit to summit K2 was Doug Scott in September 1975--only the 50th climber to succeed.
The first woman to summit the peak was Junko Tabei from Japan, months before Scott (May 1975).
To date 1,500 climbers have made it to the top.
The Mountain's Mystery surrounds deceased climber George Mallory. His body (well-preserved at frigid temps and nearly oxygen-less altitudes) was mistaken for his dead friend and climbing partner, Sandy Irvine. No one knows if Mallory and/or Irvine made it to the top or how they died. The theory is that Mallory died of unknown causes, while Irvine died from injuries sustained in a fall. Hard to clear up Mallory's cause of death without an autopsy. Unlikely to happen.