Nelson W. Diebel (born November 9, 1970) is an American former competition swimmer, Olympic champion, and former world record-holder. Diebel won two gold medals at the 1992 Summer Olympics in Barcelona, Spain. First, he won the men's 100-meter breaststroke, setting a new Olympic record of 1:01.50 in the event final. Afterward, he swam the breaststroke leg for the winning U.S. team in the men's 4×100-meter medley relay, together with fellow Americans Jeff Rouse (backstroke), Pablo Morales (butterfly) and Jon Olsen (freestyle). In the event final, the four Americans matched the world record of 3:36.93 set by the U.S. team at the 1988 Summer Olympics. Diebel attended the Peddie School in Hightstown, New Jersey. He enrolled in Princeton University, where he swam for the Princeton Tigers swim team under coach C. Rob Orr.