Two Wall Street financiers Jim Fisk and Jay Gould, together bought a significant amount of US gold in the hope of the overall price soaring and in turn being able to sell it for huge profits.
On Friday 24 September, 1869, in what became referred to as "Black Friday", the US gold market crashed and Fisk and Gould's actions left Wall Street barons bankrupt.
The losses were so significant that later the post-Thanksgiving period became associated with the name "Black Friday".
Source: The Telegraph