Known during her time as "The Witch of Wall Street," Henrietta Howland Robinson was born in New Bedford, Massachusetts, the daughter of Edward Mott Robinson and Abby Howland. Her family were Quakers who owned a large whaling fleet and also profited from the China trade. At the age of two, she was living with her grandfather, Gideon Howland. Because of his influence and that of her father, and possibly because her mother was constantly ill, she took to her father's side and was reading financial papers to him by the age of six. When she was 13, Hetty became the family bookkeeper. At the age of 15, she went to a school in Boston.
When her father died in 1864, she inherited $7.5 million ($107 million in 2010 adjusted for inflation) in liquid assets, against the objections of most of her family, and invested in Civil War war bonds.
When she heard that her aunt Sylvia had willed most of her $2 million to charity, she challenged the will's validity in court by producing an earlier will which allegedly left the entire estate to Hetty, and included a clause invalidating any subsequent wills. The case, Robinson v. Mandell, which is notable as an early example of the forensic use of mathematics, was ultimately decided against Hetty after the court ruled that the clause invalidating future wills, and Sylvia's signature to it, were forgeries.
Green conducted much of her business at the offices of the Seaboard National Bank in New York, surrounded by trunks and suitcases full of her papers; she did not want to pay rent for an office. Later unfounded rumors claimed that she ate only oatmeal that was heated on the office radiator. Possibly because of the stiff competition of the mostly male business environment and partly because of her usually dour dress sense (due mainly to frugality, but perhaps ascribable in part to her Quaker upbringing), she was given the nickname the "Witch of Wall Street".
She was a successful businesswoman who dealt mainly in real estate, invested in railroads, and lent money. The City of New York came to Hetty in need of loans to keep the city afloat on several occasions, most particularly during the Panic of 1907; she wrote a check for $1.1 million and took her payment in short-term revenue bonds. Keenly detail-oriented, she would travel thousands of miles – alone, in an era when few women would dare travel unescorted – to collect a debt of a few hundred dollars.
Some of her miserly antics included trying to check her son into a free clinic for the poor after he broke his leg, refusing to pay $200 for a horse, instead blackmailing the seller to force the price down to $60, only having two changes of clothes, never turning on heat or hot water and reportedly not even washing her hands, all to save money. After her children left home, Green moved repeatedly among small apartments in Brooklyn Heights and Hoboken, New Jersey, mainly to avoid establishing a residence permanent enough to attract the attention of tax officials in any state.
In her old age, Hetty Green began to suffer from a bad hernia, but refused to have an operation because it cost $150. She suffered many strokes and had to rely on a wheelchair. She also became afraid that she would be kidnapped and made detours to evade the would-be pursuers. She began to suspect that her aunt and father had been poisoned.
Hetty Green lived out her later years in inexpensive lodgings in Hoboken, New Jersey. When she died on July 3, 1916, she was thought to be the richest woman in America.