Hetty Green (née Robinson), nicknamed "The Witch of Wall Street" (November 21, 1834 – July 3, 1916), was an American businesswoman, remarkable for her frugality during the Gilded Age, as well as for being the first American woman to make a substantial impact on Wall Street.

She was born Henrietta Howland Robinson 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.

At the age of 33, Henrietta married Edward Henry Green, a member of a wealthy Vermont family. She made him renounce all rights to her money before the wedding on July 11, 1867. The married couple moved to Edward's home in Manhattan, but when her cousins tried to have her indicted for forgery based on the Robinson v. Mandell decision, they moved to London and they lived in theLangham Hotel. Her two children, Edward Howland Robinson "Ned" Green and Hetty Sylvia Ann Howland Green, were born there, Ned on August 23, 1868 and Sylvia on January 7, 1871.

There are many tales (of various degrees of accuracy) about Hetty Green's stinginess. She never turned on the heat nor used hot water. She wore one old black dress and undergarments that she changed only after they had been worn out. She did not wash her hands and rode an old carriage. She ate mostly pies that cost fifteen cents. One tale claims that she spent half a night searching her carriage for a lost stamp worth two cents. Another asserts that she instructed her laundress to wash only the dirtiest parts of her dresses (the hems) to save money on soap.

Ned moved away from his mother to manage the family's properties in Chicago and, later, Texas. He became an ardent philatelist and assembled one of the finest private stamp collections in the world. In middle age he returned to New York; his mother would pass her final months with him. Ned ultimately married Mabel, his long-time "housekeeper" (a former prostitute he met in Texas), of whom Hetty wholeheartedly disapproved. Despite reports that Ned was a spendthrift, and spent most of his share of Hetty's fortune, Hetty's biographer Charles Slack wrote that the $1 million yearly return on his $100 million inheritance was adequate to his most expensive needs. Slack estimated that at his death he left about the same amount of wealth that he had inherited. Most of his estate went to his sister Sylvia, while Mabel was provided for (significantly less generously) during Ned's lifetime. One of his more infamously extravagant purchases was a diamond-encrusted chamber pot.