The Pisco Sour was created by an expat American named Victor V. Morris who traveled to Lima, Peru in the early-20th century to open a saloon. (Lima was something of a boom town in those days due to the mining industry.)
A variation on the Whiskey Sour, Morris supposedly first mixed his version using the native spirit on July 28, 1904. Of course, as with the Daiquiri, attributing the origination of a relatively simple cocktail to just one person at one particular time is problematic.
But if nothing else, Morris was a significant figure in the standardization and popularization of the Pisco Sour, and for that he certainly deserve praise.