That said, I think that the original poster to this thread was probably thinking of John The Conqueroo.

Here's an excerpt from that Wikipedia page whose link I've provided:

"John the Conqueroo, also known as High John the Conqueroo, John the Conqueror, or John the Conquer root, refers to a number of roots to which magical powers are ascribed in American folklore, especially among the hoodoo tradition of folk magic. The root, in turn, is named after a folk hero called High John the Conqueror.

The root and its magical uses are mentioned in a number of blues lyrics".