He was 98 years old.
"A man larger than life, Adolph had such a huge passion and joy for swimming. He has touched many in this industry and paved the way for future athletes with his historic swimming career," a statement by Kiefer's company
Kiefer suffered from neuropathy in his legs and hands and was confined to a wheelchair, but he continued swimming daily.
"He was able to walk again in chest deep water," Olympic committee officials said.
Kiefer's record-breaking career began when he was a 16-year-old high school student. He was the first person in the world to break the one-minute mark in the 100-yard backstroke -- and months later he became the youngest member of the US Olympic team.
In 1936, Kiefer won the gold medal in the 100-meter backstroke competition at the Olympic games in Berlin, setting a record that would stand for 20 years.
Life after the Olympics
During World War II, Kiefer put a hold on his career to serve in the US Navy.
Kiefer joined the Navy's physical fitness and swimming division, where he made significant changes to the swimming training programs. He introduced his "victory backstroke" and oversaw the training of thousands of swimming instructors.
"Kiefer soon realized that several high-ranking officers didn't even know how to swim, and the Navy was actually losing more lives to drowning than bullets," a biography on his company's website
After the war, the famed swimmer focused his energy on becoming an innovator and entrepreneur.
Kiefer invented and began manufacturing swimwear, swim gear and pool equipment through his Chicago-based company, Adolph Kiefer and Associates.
He developed the first nylon swimsuits, a commercial line of floating kickboards, the PVC rescue tube that is now largely used by lifeguards, and nearly a dozen other swimming products.
"His contributions as a teacher and innovator helped save countless lives and changed the sport of swimming for the better. His passion for sport and safety was unmatched and his presence will be missed," the committee said.