During the Gilded Age of gold plates and Newport mansions, a woman in a single threadbare black dress once wrote a personal check for 1.1 million dollars to rescue New York City from ruin. That woman was Henrietta Robinson, far better known as Hetty Green, arguably the most misunderstood financial genius of her era and a fortune that would equal several billion dollars today.

This episode charts her rise from a Quaker whaling family in New Bedford, where she read stock quotes to her grandfather at age six and kept the family books by thirteen, to a disciplined value investor who bailed out the American economy. Branded the Witch of Wall Street, she was in fact a pioneer of low-overhead, research-driven investing in a world run entirely by men.

• As a teenager she spent 200 dollars on clothes and secretly invested the remaining 1,00 ...