Angostura Bitters are an absolutely essential ingredient in every bartender's arsenal, and might just be the most recognizable bottle in the world. They're used in all kinds of classic and modern cocktails, like the Old-Fashioned, Manhattan, Champagne Cocktail, and literally thousands of other drinks. The recipe for these classic aromatic bitters is a closely-guarded secret (only five people know it at a time), but we know that they're at least made from a neutral spirit with gentian root as a bittering agent and brown sugar to take the edge off.
Angostura Bitters were first developed in the early 1800s by Dr. Johann Siegert, the surgeon general in Simón Bolívar's Venezuelan army, as a health tonic to treat tropical stomach diseases. He started selling them to the public in 1854, and over the course of the next century and a half they became an indispensable ingredient in bars around the world.
According to the producers, the signature oversized label came about because one of his sons was responsible for designing the bottle, and the other designed the label separately—they realized too late that they were mismatched, but decided to keep the quirky look for the sake of recognizable branding.