Billy Mitchell is the spiritual founder of the U.S. Air Force and to this day is a culture hero to the strategic bombing cultists who have dominated the Air Force's leadership since the 1930s. Gaining a direct commission through his family's influence during the Spanish-American War, Mitchell remained in the Army after the war, gravitating to the Signal Corps and in short order becoming fascinated with aviation.
He was quickly deployed to France (as a lieutenant colonel) on the outbreak of war with Germany in 1917, and just as quickly gained a reputation for courageous and flamboyant leadership. He was quickly promoted to brigadier general and head of all American air units in France. By the time of the St. Mihiel offensive in September 1918, Mitchell planned and led over 1500 Allied aircraft in the first combined air-ground offensive ever. He ended the war as a highly decorated celebrity, but had also managed to antagonize quite a few of his peers within the Army.
After the war, Mitchell retained his wartime rank of brigadier general but was denied command of the Air Service, which was given to one of General Pershing's West Point classmates with the aim of keeping the air service as a support arm within the Army.* Mitchell continued to agitate for a separate Air Force and did everything he could to keep aviation in the public eye by encouraging Army pilots to get involved in air races and attempts to set aviation records. He also continued to antagonize his superiors with constant criticism of the War Department and the Navy Department for paying insufficient attention to aviation and its possibilities for future warfare. These attempts came to a head in 1921 as Mitchell successfully lobbied for a test of his bombers against Navy ships, and nearly got cashiered for his pains until Congress forced the issue by passing resolutions demanding that the tests take place.
The tests were a success. Mitchell's bombers, using tactics he had developed (with useful suggestions by Russian emigre Alexander Seversky) sank a captured German destroyer and light cruiser, and then the captured battleship Ostfriesland, which was considered unsinkable. Still, Mitchell had managed to further alienate his superiors in the Army, who were trying to smooth relations with the Navy at the time, and he wound up being sent on a tour of Hawaii and Asia to get him out of the headlines. His report, which predicted an attack on Pearl Harbor by air (but by land-based bombers, not aircraft carriers, which he considered useless) stirred up more controversy, and earned him a demotion to colonel and transfer to a staff position in San Antonio.
This exile failed to keep Mitchell out of the news. Following the loss of three seaplanes en route to Hawaii and the horrific crash of the dirigible Shenandoah, Mitchell accused senior Army and Navy officials of incompetence and malfeasance bordering on treason. This caused President Coolidge to order his court-martial, which found him guilty of insubordination and sentenced him suspension from active duty for five years without pay. (It was claimed by Fiorello H. LaGuardia, a friendly witness, that he found Douglas MacArthur's "not guilty" ballot in a wastebasket after the trial.) Mitchell resigned in 1926 instead, intending to continue campaigning for the cause of a separate Air Force, but found his influence diminished due to his civilian status.
He died in 1936 of heart failure and the flu, too soon to see his dream of a separate air force fulfilled. The Air Force named the B-25 Mitchell bomber after him, the only time an American aircraft has been named for a specific person, and President Roosevelt promoted him posthumously to Major General on the Army Air Corps retired list.
*see the Luftwaffe and the Soviet Air Force for examples of this