Complex sentence: The first successful use of it was by David Berkoff at the 1988 Olympics, where he swam most of the 100 m backstroke race underwater and broke the world record on the distance during the preliminaries.
Split into simpler sentences: The first successful use of it was by David Berkoff. At the 1988 Olympics, he swam most of the 100 m backstroke race underwater and broke the world record on the distance during the preliminaries.