You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For consistency, answers should be in all lower cased letters.
--------
Question: Category: HEY, "D.J." 
Clue: James Buchanan Brady's gem of a moniker

Answer: diamond jim


Question: Category: 19th CENTURY BUSINESSMEN 
Clue: In 1873 he founded the J. Edgar Thomson works near Pittsburgh, naming the steel mill for the Penn. railroad president

Answer: carnegie


Question: Category: THE CIVIL WAR 
Clue: On March 12, 1864 he was promoted to commander of all Union forces

Answer:
ulysses s. grant