Moscow mule maybe not the first vodka-based cocktail. There is no doubt that it is the most famous one. The unusual and unexpected combination of Vodka and ginger beer within a copper mug creates a legend that leaded the Vodka burst in 1940's.
Vodka was a relatively unknown spirit outside Russia that time. People preferred drink with little power. Vodka is something too strong for them. At that moment John Martin was in charge of a company named Heublein. He had just got the Smirnoff brand, which had its own origins in Moscow in the mid 1860s, and production right for his company. But things did not go smoothly as he wished. The market refused Russian style drink. He was just in struggling to increase the selling of this spirit.
Some stories about Moscow Mule told us: One day Martin had just stepped into Cock'n'Bull bar which was located in Sunset Boulevard to meet his friend Jack Morgan, who also acted as the manager of this bar. Morgan had a frustrate selling of his homemade ginger beer, just the same as Martin. That day is the beginning of the Moscow Mule legend. And all debates of who invented this cocktail always came back to this monent.
There were at least three versions of the third person who witnessed the creation of Moscow Mule.

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  The girlfriend of Morgan,according to John Martin's interview video by WSJ.


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  The president of Pierre Smirnoff Heublein's Vodka Division, Rudolph Kunett. According to the book" Straight Up or On the Rocks: The Story of the American Cocktail" by Grimes William.


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  A friend X of them who had inherited a large collection of copper mugs. According to the book " Field Guide to Cocktails: How to Identify and Prepare Virtually Every Mixed Drink at the Bar " by Rob Chirico.

That was just my favorite part, but also the most doubtful part.It happened all too obvious and dramatic to begin a legend. Martin and Morgan had their minds on their vodka and ginger respectively. Martin sparked some inventive genius to mix these two drinks together, and shake with a massive dose of ice cubes. Adding a wedge of lime, then the miracle is made. So you can barely concern the establishment of the Moscow Mule as an invention, but likely an accident. Because of the kick of the ginger beer, this cocktail was nicknamed as Mule initially. After four or five grounds, the mixture was finally christened as Moscow Mule.
Another story about Moscow Mule was totally different. According to a 2007 article in the Wall Street Journal penned by the reliable Eric Felton. The Cock 'n' Bull's head bartender Wes Price also claimed the recipe is his idea. And I have a tendency to believe a bartender over a marketer; I believe the drink must be created by some bartender. Because no one participated in the original creation story ever explained where the name came from.
Nonetheless, it's really quite obvious. The "Mule" is, itself, a class of mixed drink, which refers to liquor mixed with lime and ginger beer. Only bartenders would know not only name it properly refers,but also how to mix another ingredient to create a new mule.