It is believed that this drink was created by Harry Craddock, head bartender of the Savoy in London. Harry was an American bartender who decided to ply his trade overseas when American Prohibition hit. He joined the Savoy in 1920 and in 1930, he came out with “The Savoy Cocktail Book”, which was fairly popular, even in America where Prohibition was still in effect, although many realized it was on its last legs.
Stir with ice and strain into a cocktail glass
Source: "The Savoy Cocktail Book" by Harry Craddock (1930)