Arnold was an American general officer holding the grades of General of the Army and General of the Air Force. Arnold was an aviation pioneer, Commanding General of the U.S. Army Air Forces in WWII; the only Air Force general to hold five-star rank, and the only person to hold a five-star rank in two different U.S. military services. Arnold was also the founder of Project RAND, which evolved into one of the world's largest non-profit global policy think tanks. Instructed in flying by the Wright Brothers, Arnold was one of the first military pilots worldwide.