Question: William Corcoran Eustis (July 20, 1862 - November 24, 1921) was a captain in the United States Army and the personal assistant to which General of the Armies during World War I, who was was a senior United States Army officer, that had a nickname of "Black Jack"?
{'answer': 'John Joseph "Black Jack" Pershing', 'supporting_facts': [['William Corcoran Eustis', 0], ['John J. Pershing', 0]]}