According to drink authority Barnaby Conrad III, its origins are obscure and much debated. He posits, however, that the probable first recipe for this holy grail is in an 1896 manual by Thomas Stuart titled “Stuart’s Fancy Drinks and How to Mix Them.” It was called a “Marguerite Cocktail,” and into it went one dash of orange bitters, two thirds Plymouth gin, and one third French vermouth. “By 1900,” Conrad writes, “the word Martini was in common usage among bartenders on both sides of the Atlantic.”
The origin of the Martini, discovered in The Perfect Martini by Christopher Buckley on The Daily Beast