There are many stories about Cocktail Martini Dry. One of them is for the bartender Martini di Arma di Taggia, the Hotel Knickerbocker, New York (1911). He mixed London Dry Gin and vermouth Noilly Prat in proportion 1:1 and added a few drops of orange bitters. He cooled the drink and serve it in another chilled cocktail glass. It is argued that the classical olive was added by a customer for diversity.
One thing is clear, this is one of the most famous cocktails and will remain so.