Measuring the relative wealth of titans who lived in different eras is an art, not a science. But that has not deterred people from trying. In the 1996 book "The Wealthy 100," authors Michael Klepper and Robert Gunther ranked the net worth of 100 wealthy Americans by percentage of gross national product. Two years later, American Heritage magazine compiled a list of the 40 richest Americans in history, based on 1998 dollars. All agreed that John D. Rockefeller was No. 1. And both listed Hetty Green as the richest woman in America. Dubbed "America's First Female Tycoon," or the "Witch of Wall Street," Green deservedly earned a place in the pantheon of American titans. Unfortunately, she is better known for her eccentricities and miserly ways—and she was as tightfisted as a bare-knuckled boxer—than for her unprecedented accomplishments in what was an exclusively male domain: finance.