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The B-52 cocktail is a layered shot composed of coffee liqueur (Kahlúa), Irish cream (Baileys Irish Cream), and Grand Marnier (in later versions replaced with triple sec or Cointreau). When prepared properly, the ingredients separate into three distinctly visible layers (due to their relative densities). The origins of the B-52 are not well documented, but one claim is that the B-52 was invented by Peter Fich, a head bartender at the Banff Springs Hotel in Alberta, Canada. Fich named all of his new drinks after favorite bands, albums, and songs, and he supposedly named the drink after the band of the same name, not directly after the US B-52 Stratofortress bomber or the beehive hairstyle after which the band was named. One of Fich's first customers for a B-52 owned restaurants in various cities in Alberta, and they liked the drink so much that he put it on the menu, leading to the perception that the B-52 originated at the Keg Steakhouse in Calgary, Alberta in 1977. The B-52 is also rumoured [by whom?] to have been created by Adam Honigman, a bartender at New York City's Maxwell's Plum.

Source: Wikipedia