Sheck Exley

• One of the pioneers of cave diving
  
• A pioneer of extreme deep scuba diving
  
• Wrote two major books on the subject: Basic Cave Diving: A Blueprint for Survival[3] and Caverns Measureless to Man
  
• First chairman of the Cave Diving Section of the National Speleological Society.
  
• Died at age 45 while trying to set a depth record by diving the world's deepest sinkhole, Mexico's 1,080-foot (330 m) deep, Zacatón, a fresh water cenote.
  
• Exley Wiki