We'll never know with absolute certainty when the Martini was born, or who was its creator, but my research points toward the drink being a direct descendant of the Manhattan. Recipes for the Martini started to appear in cocktail books in the late 1800s, and many of them were very similar, and sometimes identical, to recipes for the Martinez, a cocktail that appeared in print in the 1880s and was often described as “a Manhattan, substituting gin for the whiskey.” Thus, theoretically at least, the Martinez was a variation on the Manhattan.
The first Martinis were made with Old Tom (sweetened) gin. sweet vermouth, bitters, and maraschino liqueur, and even when the the Dry Martini came into being, circa 1906, it contained bitters as well as dry gin and dry vermouth. Orange bitters remained an ingredient in Dry Martinis right through tot he 1930s, but by the late 1940s the drink was being made with just dry gin and dry vermouth, and the amount of vermouth used was getting smaller and smaller.
Many of the first Dry Martinis were made with equal amounts of gin and vermouth, but by the early 1950s some bartenders had already started to use atomizers to dispense the vermouth into the rink, and bitters had been dropped from the recipe. So the Dry Gin Martini, as we know it today, has been around for over half a century.
These days, many cocktails are known as Martinis even though they contain no gin (or even vodka) and vermouth, dry or sweet, is nowhere to be found in the recipe. These drinks are merely cocktails, but for one reason or another, during the cocktail craze of the 199s, they were dubbed Martinis. Martini, therefore, has become another word for a cocktail of any kind, just as long as it can be served in a Martini glass. Many purists abhor this phenomenon. …
Martinis should be stirred and not shaken, simply because the sight of a bartender lovingly stirring this drink for at least twenty to thirty seconds is something that people enjoy. Stirring for approximately 30 seconds will yield a drink that's just as cold as one that has been shaken for 10 seconds—it's worth the time. Shake it if you must, and if a customer requests that the drink be shaken, then that's how it should be made. Never use gin or vodka from the fridge or freezer, since the spirit will be too cold to melt enough ice—a very necessary ingredient in a well-made Martini.
You can make Martini's with white rum or tequila, but they aren't very good drinks. Gin marries perfectly with vermouth, and vodka, too, is a good base spirit to use. The ratio of gin or vodka to vermouth is entirely up to your discretion, but although many people prefer a mere hint of vermouth in their Martinis, I suggest that you start by using one part vermouth to each four or five parts base spirit. Taste the drink, and on future occasions you can alter the proportions to suit your preferences. …
Choosing specific bottlings of gin, vodka, and vermouth is of tantamount importance when making a Martini, and the ratio of vermouth to base spirit can vary with your choice of gin or vodka. Some gins—Bombay, Leyden, and Gordon's, for instance—aren't as intensely perfumed and dry as such bottling as Taqueray, Beefeater, Boodles, Van Gogh, Junipero, or Plymouth. The “softer” bottlings, therefore, will need less vermouth than the later category of gins. The same applies, though to a far lesser extent, to vodkas. These spirits, however, don't vary enough in character for the ratios to be differentiated from one bottling to another, so it's pretty futile to attempt to give guidance in this respect. Experiment until you find your favorite ratio.
Vermouths, too, vary from one label to another, though most of the recognizable brands, such as Noilly Prat, Cinzano, and Martini & Rossi, are fine products. …
As for garnishes, I prefer a pimiento-stuffed olive in a Gin Martini and a lemon twist in a Vodka Martini, but many new garnishes, such as olive stuffed with almonds or anchovies, are not available, and you should experiment with whatever takes your fancy. Always remember that the Martini is a purely American drink, and therefore people should be able to exercise freedom of speech when requesting one: If somebody wants a Gin Martini made with with equal parts gin and vermouth, a splash or two of bitters, and a pickled tomato for a garnish, then that's the way the Martini should be made.
Stir and Strain into a chilled cocktail glass. Add the garnish.