What is the alcohol in an original Old Fashioned cocktail?

The Old Fashioned is a cocktail made by muddling sugar with bitters, then adding alcohol, such as whiskey or brandy, and a twist of citrus rind. It is traditionally served in a short, round, tumbler-like glass, which is called an Old Fashioned glass, named after the drink.

By the 1860's, it was common for orange curaçao, absinthe, and other liqueurs to be added to the cocktail. The original concoction, albeit in different proportions, came back into vogue, and was referred to as "old-fashioned". The most popular of the in-vogue "old-fashioned" cocktails were made with whiskey, according to a Chicago barman, quoted in the "Chicago Daily Tribune" in 1882, with rye being more popular than Bourbon. The recipe he describes is a similar combination of spirits, bitters, water and sugar of seventy-six years earlier.

The original Old Fashioned recipe would have showcased the whiskey available in America in the 19th century: Irish, Bourbon or rye whiskey. But in some regions, especially Wisconsin, brandy is substituted for whiskey (sometimes called a Brandy Old Fashioned). Eventually the use of other spirits became common, such as a gin recipe becoming popularized in the late 1940's.