Green turned a small fortune inherited from her parents into a huge one. Her investment style was conservative, but canny; she favored railroads and real estate, and always kept substantial cash reserves. She lent but did not borrow. Referred to (behind her back) as the "Witch of Wall Street," she was known for two things: her ability to make money and her inability to spend it.
Perhaps it is not true that she spent an entire night looking through her house for a two-cent stamp, but her stinginess was legendary. She had a single black dress that she would wear until it wore out, and disdained heat and hot water. She worked out of space at a bank, surrounded by stacks of securities, unwilling to pay rent for a room of her own. She re-used envelopes and ate oatmeal for lunch. In old age, when she suffered a hernia, she refused to have an operation: It would have cost $150. When she died, Green's fortune was estimated at $100 million (about $2 billion in current dollars).