The cocktail combining bourbon, sweet vermouth and Campari is the Boulevardier.
The drink is commonly credited to Erskine Gwynne, an American writer who founded the Paris magazine The Boulevardier. Harry McElhone included a Boulevardier recipe in the 1927 book Barflies and Cocktails, associating it with Gwynne.
Its equal-parts formula resembles a Negroni, but whiskey replaces gin. Many modern recipes use bourbon, while rye whiskey is also common and gives the drink a drier, spicier character. The combination is usually stirred with ice and served chilled, often with an orange twist.
The Boulevardier is not simply a Manhattan with Campari added. A Manhattan traditionally uses whiskey, sweet vermouth and bitters, whereas the Boulevardier’s defining bitter component is Campari. The Americano, another related drink, uses Campari and sweet vermouth with soda water instead of whiskey.