Clark Stanley (born c. 1854 in Abilene, Texas, according to himself; the town was founded in 1881) was an American herbalist and quack doctor who marketed a "snake oil" as a patent medicine, styling himself the "Rattlesnake King" until his fraudulent products were exposed in 1916, popularizing the pejorative title of the "snake oil salesman".

With the help of a Boston druggist he began marketing his product at Western medicine shows.

In 1917, subsequent to the passage of the Pure Food and Drug Act in 1906, Stanley's concoction was examined and found to be of no value.

It was found to contain mineral oil, a fatty compound thought to be from beef, capsaicin from chili peppers, and turpentine.

[5] The term "snake oil" would go on to become a popular euphemism for ineffective or fraudulent products, particularly those marketed as medicines or cures.