Karl's parents, August and Karoline, had just returned from America when he was born. They had made a good life for themselves in the USA, but returned to Germany because of August's ill health. He died two years later, and Karl's mother Karoline was forced to bring Karl up and earn a living. She first worked for the local railroad before opening a grocery shop. She worked hard and earned a good living, which she used to pay for Karl's education.
When he left school, Karl became a mechanic and trained at the "Süddeutsche Automobilfabrik Gaggenau" until 1910. He already had a passion for cars, at 13 he drove for the first time, and in 1906 he applied for a driver's license. So at 15 he became one of the first and youngest Germans ever to get one. His engineering abilities stood him in good stead during the exam as the car broke down three times. Each time Karl fixed it.
He first raced in 1907, still only 16 years old, driving a SAP built by the Süddeutsche Automobilfabrik Gaggenau, where he was apprenticed. In the Berlin to Stuttgart race Kappler won twelve of a race's thirteen stages. There were no maps, so Kappler had to keep asking for the best route. There were also no petrol stations, so fuel had to be purchased from local pharmacies.
In 1911 he went to work for Benzwerke Gaggenau and was promoted in 1915 to a fulltime engineer working on the design and construction of early airplanes.
He established a good reputation and was hired by the airplane company "Automobil und Aviatik AG" in Leipzig in 1917, to head up their large airplane division. In Leipzig, Kappler airplanes were some of the most feared in World War I. However with the Versailles Treaty, Germany had to give up aircraft production. Kappler lost his job and returned to Gernsbach where he sold Daimler Benz cars and opened a shop selling tires.
In 1922 he won a race in Baden-Baden and, now 31, started to gain public recognition for his driving. At the wheel of Benz cars, he won many races over the following months and years. Praised by the Press, they called him "one of the oldest, most experienced and most successful drivers".
In the 1920's he drove "Simson Supra" cars, and by 1927 he had won 200 races. Kappler often raced in two different classes, competing in both racing and sports cars by just changing the body.
In 1927 driving a Bugatti T35, he survived two bad accidents. In one the spectators even though that he was dead. He continued winning races until his retirement in 1930 at the age of 40 when he sold the Bugatti to Prince von Leiningen..
However that was not the end of his competition driving and he turned to long distance rallies and in 1933, he famously drove from Berlin to Monte Carlo in 25 hours.
Around the time of the II World War, he faded from the scene and died in 1962, aged 71 in relative obscurity.