The Martini has been so famous and popular for so long, it should have a history as clear as it looks, right? If someone served you a Martini as murky as its history, you'd send it back. Its history is a mystery. Combining gin and vermouth in drinks such as the Martinez wasn't unusual in the 19th century. As time went by, the drinking public began to favor drier gins, and by 1896 what we now know as the Martini mixed dry gin and dry vermouth with an emphasis on the gin.
2.5 ounces gin (sorry James Bond)
.5 ounces dry vermouth
1-2 dashes orange bitters
Combine in a mixing glass with ice, stir (sorry again Mr. Bond), and strain into a martini glass. Lemon peel garnish optional.
The world’s most famous fictitious Martini consuming Englishman drinks his with vodka (and shaken). The world’s most famous real Martini consuming Englishman, Winston Churchill, drank his with gin. Originally I only drank vodka Martinis, but since I found I like certain gins, I'm not as picky. Whatever you do, use fresh vermouth. I can't emphasize that enough. Feel free to experiment with how dry you like your Martini (more dry means less vermouth). Bitters aren't necessary, but they add a little zest to a clear, gin based cocktail.
There's nothing mysterious about a Martini. All you have to do is savor one.