The ORIGINAL Martini (first called a Martinez) called for 4 parts to 1 part. That's 4 parts VERMOUTH to 1 part gin! And it was red Italian sweet vermouth. This Martini was created sometime between the years 1862 and 1876. It was made with an aromatic bitters called Boker's bitters. The closest thing we have today...... Fee's Aromatic Bitters. This version used Old Tom Gin, because there was no such thing as London Dry when the cocktail was introduced. Old Tom was very Junipery, a little golden, and rather sweet. Take some Bols Genever Gin, mix with twice the volume Tanqueray, and say, sweeten with a couple teaspoonsful of sugar, and you have a rough approximation. (There is a brand of Old Tom that's still produced -Boord's makes it- but it tastes just like London dry to me.) Next, Orange Bitters were used in preference to Bokers, London dry gin in place of Old Tom, and the proportions went to equal parts. Then, the Dry Martini made its debut..... equal parts London Dry and FRENCH (Dry, or white) vermouth and orange bitters.

What IS lost to history is exactly when the olive entered the picture. I don't know, and never met anyone who did. The original had the cherry. By 1900 a twist. Certainly by the 20s in England an olive was in place, but how it happened is a mystery."
-Credit to "Dr. Cocktail" at AOL.

The Oxford English Dictionary gives the earliest use of the word Martini as 1894 and states that the word comes from Martini and Rossi Vermouth.
(The ONLY one I will use!)
Vermouth: Hippocrates first created it in 460 BC ! It is a complex mix of herbs...