Though Fisk was admired by the working class of New York and the Erie Railroad, he achieved much ill-fame for his role in Black Friday in 1869, where he and his partner Jay Gould befriended the unsuspecting President Ulysses S. Grant in an attempt to use the President's good name in a scheme to corner the gold market in New York City.

By his shrewd dealing in army contracts during the Civil War, and, by some accounts, cotton smuggling across enemy lines—in which he enlisted the help of his father—he accumulated considerable wealth, which he soon lost in speculation.

[1] Fisk and Gould carried financial buccaneering to extremes: their program included an open alliance with New York politician Boss Tweed, the wholesale bribery of legislatures, and the buying of judges.

She tolerated Fisk's many extramarital affairs, perhaps because she was happy living with her “childhood friend and inseparable companion,” Fanny Harrod, in Boston.

Mansfield eventually fell in love with Fisk's business associate Edward Stiles Stokes (1840–1901), a man noted for his good looks.

Increasingly frustrated and flirting with bankruptcy, Stokes confronted Fisk in New York City on January 6, 1872, in the Grand Central Hotel[4] and shot him twice, in the arm and abdomen.

Some twenty thousand people came to pay their respects, with five times as many more individuals waiting in the streets to gain entrance.

Fisk was vilified by high society for his amoral and eccentric ways and by many pundits of the day for his business dealings; but he was loved and mourned by the workingmen of New York and the Erie Railroad.

He was known as "Colonel" for being the nominal commander of the 9th New York National Guard Infantry Regiment, although his only experience of military action with this unit was an inglorious role in the Orange Riot of July 12, 1871.

[7] The circumstances surrounding his murder were dramatized in the CBS radio program Crime Classics on June 29, 1953, in the episode entitled "The Checkered Life and Sudden Death of Colonel James Fisk".

[8] The rumor quickly spread to Helsinki, the capital of the Grand Duchy of Finland at the time, and then to Turku, reaching these cities through newspapers in July 1872.