This bitters herb

There's no accounting for some people's taste, but the cocktail hour nods to Don Draper, Italy and the Queen of England (and Her Royal Navy);

...there is now a definite trend towards bitter drinks. People are ordering whisky or gin-based drinks paired with vermouths. And there is growing interest in the US, UK and other European nations in Italian amari.

These complex, herbal, bittersweet drinks, with names like Averna, Ramazzotti, Montenegro and Fernet Branca, are usually consumed as aperitivi or digestivi - drinks thought to either encourage the appetite before dinner or help with digestion afterwards.

The Mad Man won't take a Manhattan, but an Old Fashioned;

[Angostura] bitters is the key ingredient in pink gin, the traditional officers' cocktail in the Royal Navy. It's also the bedrock of famous cocktails, including the Old Fashioned, beloved of Mad Men's Don Draper, and the Manhattan. 

Even Her Majesty (and Her Secret Service) is up on the fashion;

Many James Bond fans attempt to recreate the Vesper Martini from Casino Royale. Bond asks for it to be made with strong gin, vodka and the bitter Kina Lillet. Lillet took out much of the bitter quinine in the 1980s and fans tend to use Cocchi Americano Italian vermouth instead.

And the Queen has followed in her mother's footsteps by drinking gin and Dubonnet - the quinine-bittered French aperitif. Just a few years ago, her choice was seen as unusual.

Cheers.