Which individual was a former race car driver?

Eddie Rickenbacker is the correct choice because he was not only a famous World War I flying ace but also had a successful career as a race car driver prior to his military service. Rickenbacker participated in auto racing during the early 20th century, even winning several races and becoming renowned in that field. His transition from racing to aviation highlights the diverse talents and interests he possessed, contributing to his later achievements as a pilot and military leader.

In contrast, Glenn Curtiss was primarily an aviation pioneer known for his contributions to airplane design and development. Alfred von Richthofen, famously known as the "Red Baron," was a distinguished German fighter pilot during World War I and had no significant background in auto racing. Frank Whittle is most celebrated for his invention of the jet engine, focusing heavily on advancements in aircraft propulsion, with no connections to automotive racing.