Sugar is the traditional sweetener used with bitters and whiskey in an Old Fashioned cocktail.
The basic drink combines a spirit, sugar, water, and bitters. Modern recipes commonly use bourbon or rye whiskey, though the older formula was not originally restricted to one particular spirit. Orange peel is a widespread garnish, but the essential structure is the balance between spirit, sweetness, dilution, and aromatic bitters.
The name “Old Fashioned” emerged in the late nineteenth century as drinkers asked bartenders for cocktails made in an older, simpler style. It is therefore better understood as a preparation format than as a single immutable recipe. Some versions use a sugar cube muddled with bitters and water; others use simple syrup. Fruit-heavy versions became popular in parts of the United States, but they are regional interpretations rather than the core historical formula.