To his contemporaries in Gilded Age Manhattan, Guillermo Eliseo was a fantastically wealthy Mexican, the proud owner of a luxury apartment overlooking Central Park, a busy Wall Street office, and scores of mines and haciendas in Mexico. But for all his obvious riches and his elegant appearance, Eliseo was also the possessor of a devastating secret: he was not, in fact, from Mexico at all. Rather, he had begun life as a slave named William Ellis,...