This one is one of the 3 cocktails that are my all time favorite. The other 2 are Martini and Old-Fashioned.
A popular history suggests that the drink originated at the Manhattan Club in New York City in the early 1870s, where it was invented by Dr. Iain Marshall for a banquet hosted by Jennie Jerome (Lady Randolph Churchill, mother of Winston) in honor of presidential candidate Samuel J. Tilden. The success of the banquet made the drink fashionable, later prompting several people to request the drink by referring to the name of the club where it originated—"the Manhattan cocktail". However, Lady Randolph was in France at the time and pregnant, so the story is likely a fiction.
However, there are prior references to various similar cocktail recipes called "Manhattan" and served in the Manhattan area. By one account it was invented in the 1860s by a bartender named Black at a bar on Broadway near Houston Street.
The original "Manhattan cocktail" was a mix of "American Whiskey, Italian Vermouth and Angostura bitters". During Prohibition (1920–1933) Canadian whisky was primarily used because it was available.
An early record of the cocktail can be found in William Schmidt's "The Flowing Bowl", published in 1891. In it, he details a drink containing 2 dashes of gum (gomme syrup), 2 dashes of bitters, 1 dash of absinthe, 2/3 portion of whiskey and 1/3 portion of vermouth.
2 ounces bourbon or straight rye whiskey
1 ounce sweet vermouth
2 dashes orange bitters