"Black Jack" Pershing earned his nickname from his service with the 10th Cavalry during the Indian Wars and the Spanish-American War, where he was cited for bravery during the Battle of San Juan Hill*.
His service with the "buffalo soldiers" of the 10th was held against him by the cadets of West Point when he returned there as a tactics instructor, and in fact they called him "Nigger Jack" - but not, of course, to his face.
Pershing would go on to command troops with distinction in the Philippine Insurrection before being promoted to brigadier general by President Roosevelt after his return from Japan, where he had served as military attache and observer of the Russo-Japanese War. This promotion was quite controversial since it jumped Pershing three grades over the heads of hundreds of senior officers at a time when the Army promoted almost exclusively by seniority. Pershing went on to observe the Balkan Wars before returning to command the 8th Cavalry at Fort Bliss; he would lead the 8th in futile pursuit of Pancho Villa during the Punitive Expedition.
When America entered World War I against Germany, President Wilson's first choice for commander of the American Expeditionary Force was Frederick Funston, hero of the Philippine Insurrection. Unfortunately, Funston died of a heart attack in February 1917, and after a short interview, Wilson promoted Pershing from major general to full general, the first time anyone had held the four-star rank since Phil Sheridan. Secretary of War Newton Baker gave Pershing carte blanche to run the AEF as he saw fit, and Pershing responded by being very careful to avoid political or other distractions. This explains his refusal to use the black National Guardsmen of the 93rd Division.** Despite his earlier successful service with colored troops, he was aware of Wilson's racist attitudes and the political debts Wilson owed to Southern Democrats, and wished to avoid controversy.
Pershing is best known for insisting that (white) American units fight united under American commanders and not be parceled out as reinforcements for British and French units that had been bled white by three years of trench warfare. He also founded the Military Police Corps and invented a new kind of combat boot more suitable for the trenches of the Western Front. At the end of the war, all of the AEF's successes were credited to Pershing, and he was promoted to General of the Armies, entitling him to wear four gold stars (in place of the conventional four silver stars of a full general) and outrank all other officers, even the five-star generals created during World War II. Like those generals, Pershing remained on active duty until his death in 1948, although he took no active part in Army affairs after retiring from active service in 1924.
Perhaps his most durable legacy to the Army were the junior officers he trained in the early 20th century who rose to take staff and command billets in the AEF, such as George S. Patton, George C. Marshall, and Douglas MacArthur. These officers would later lead the American Army to victory in World War II.
*This citation was upgraded to a Silver Star in 1932.
**The 93rd never served as a complete division; its regiments were issued French arms and equipment and used separately in French divisions, where they earned numerous decorations.