They say the sun never set on the British Empire. That would explain, among other things, the gin and tonic.

No other drink counters oppressive heat better than a gin and tonic. The Gatorade of British colonial days, it was what allowed Englishmen to join mad dogs out in the noonday sun. To my taste, a brisk gin and tonic cuts the dust far better than its closest competitor, the rum-based umbrella drink. That, along with its hard-won stature as a cultural icon, has made the gin and tonic one of the greatest cocktails of all time.

If it was British policy that once made much of the world British, it was British gin that made far-flung outposts feel like home to the Brits. Caribbean Rum, Cachaca (its South American counterpart), and whiskey from America became popular when they were brought back to London. But gin, although not quite born under the Union Jack, was adopted early on and became part of the family. So while the Brits enthusiastically imported spirits from their colonies, they were more comfortable doing things the other way around, sending gin along with the colonists and/or making it in situ.

Meanwhile, colonists in tropical places had already acquired a taste for sweetened quinine water, an infusion of the medicinal cinchona plant, which was called tonic because of its effectiveness in warding off malaria. When gin met this oddly bittersweet quinine tonic, magic happened; the odd couple brought out the best in each other and became a famous partnership. Of course, quinine is only a flavoring in modern tonic, which is decidedly sweet and also carbonated. But a good one (Schweppes is my favorite) retains enough of that bitter cinchona flavor to sharpen the drink’s edge and make it that much more thirst quenching. In a small but important way, the mixture of gin and tonic became a pillar of the Empire.

Thus the marvelous medicinal spirit that was perfected by the Dutch and became British in the gin-soaked depravity of 17th century London traveled the world and was transformed in equatorial lands, ultimately returned to the capital in triumph as one of the all-time classic cocktails.

Consider some of its many facets. On one hand, it’s so utterly Raj, so "Jewel in the Crown," a cocktail to be sipped at sundown in Rajasthan while admiring the day’s trophies, something to be holding while being photographed with one foot on a dead tiger, a drink to erase the day’s heat and welcome the pleasures of evening with the wily vapors of an iced, exquisitely perfumed spirit. I associate that expression with florid gins such as Bombay and its finer, more subtly exotic sibling, Sapphire.

On the other hand, its evocation of distant India can be a background note in a more immediate impression of English sophistication, in a wood-paneled London club or a San Francisco watering hole. For that more urban gin and tonic I think of drier, edgier London dry gins such as Gordon’s and Beefeater.

Cultural associations aside, it’s also just a damn fine drink on its own merits. And that opens a whole new world of subtly unique gins that have appeared in the last few years. The ultimate flavored vodka, gin is made by infusing a colorless, odorless spirit with uniquely scented, and occasionally colorful "botanicals." These go well beyond the fundamental juniper berries to include such plants and parts of plants as (to choose a few examples) angelica, coriander, grains of paradise, licorice, cassia, orrisroot, bitter almonds, and citrus peels. And a new generation of distillers has gotten even more creative, introducing previously unheard-of notes from plants like iris, peppermint, and kava kava.

MULTICULTURAL CLASSIC
As noted above, gin started out Dutch, as the juniper-scented Genever. But it has become decidedly international in recent years. One of the best is produced in France and named after a Portuguese explorer. Another has a Dutch name but is distilled in Scotland. Russia produces a beauty. There’s even a gin from New Zealand that employs a traditional Maori herb in its distillation.

Hendricks is a name that makes me think of the Dutch East India Company — except that it’s distilled in Scotland. And those intrepid seagoing profiteers from Holland, civilized as they were, probably would not recognize the nouveau flavor that distinguishes Hendricks, a piercing redolence of cucumbers. They certainly would recognize the color of Magellan. It’s a shade of blue that the great 16th century navigator saw as he gazed toward the unknown horizon from the deck of the Victoria. The French gin that bears his name is the most-lovely aquamarine. It comes by that hue from the infusion of blue iris petals, which also lend a floral quality to the flavor. In fact, it’s the only naturally blue spirit I’ve ever seen.

Plymouth Gin, a new incarnation of an 18th century brand that adheres to an artisan expression of the old-time recipe, is a gently floral, high-toned flavor informed by orrisroot. Tanqueray Ten has a distinctly orangey-flavor profile. South Gin, from New Zealand, gains a marvelous herbal zing from a touch of kava kava. Russia’s Vedrich is similar to Plymouth but a little sharper, perhaps due to the inclusion of peppermint in the botanical roster.

A classic cocktail is all about a few distinctive ingredients in perfect balance. As we’ve seen, the classic gin and tonic is all about fine gin and an ever-so-slightly bitter tonic. It also has what I’d call a working garnish, the bright note of citrus as in a wedge of lemon or lime. But I go farther than that. To me, the perfect gin and tonic has more than a touch of lime.

THE FINAL TWIST
This third ingredient has all the historical authenticity of the first two. Lime has its place in the annals of British exploration and colonization, as well. As a source of concentrated vitamin C, lime juice sailed on every ship in the British navy and the Dutch East India Company — hence the British seaman’s enduring nickname, Limey.

That’s my nickname, too, among a certain group of cocktail purists who believe that the classic gin and tonic is made with lemon. They also call me a heretical hedonist. But I’ve noticed that most of them have gradually taken to making their gin and tonics the way I do: with the juice of half a lime, freshly cut and squeezed for the purpose.

I believe that the noble lime has a more complex and engaging flavor than any other fruit, excepting wine grapes. Indeed, as a wine grape is more flavorful and acidic than a table grape, the lime has twice the acidity of the lemon and considerably more sweetness, giving it a superbly intense impact on the palate. And it’s a wonderful complement to gin, that most complex and engaging of spirits. I’m referring primarily to our most common lime, citrus latifolia, the small, seedless lime often called Persian or Tahiti lime. But the same holds true for the seeded lime, citrus aurantifolia, better known as the Key lime.

Now, here’s something to file under "Arcane Secrets of the Universe": Ripe limes are not green. They’re more yellow, like unripe lemons. I know, it’s counterintuitive. That’s why most of us, including me until recently, put a lot of effort into pawing through the lime bin at the store looking for that elusive dark-green lime without any hint of yellow on it. But once you compare the relatively pale scent and flavor of that dark-green beauty with the vivid sensory explosion from the washed-out-looking yellow lime, you’ll understand. The balance of sweetness and tang in a ripe lime, its high-toned perfume and fully developed flavor, make the unripe lime taste, well, green.

Who knew? And does this little factoid matter? It does to a gin and tonic devotee like me. The fully mature lime flavor expands the universe of clarity and bright, defined flavors; it seems to help the gin bloom into full complexity, summoning whole constellations of botanical stars to gleam on the palate. All that, from the juice of a little yellow-green fruit, the jewel in the great cocktail’s crown.

Like all true classics in any genre, the gin and tonic swiftly exceeded its raison d’etre and established itself as a quaff not only for all seasons, but for all eternity. It stands as a demonstration that perfection is not rigid, but fluid, and it has the power to make one believe, for the first few sips at least, that the real horror of global warming is the prospect of no more ice for cocktails. That’s why the gin and tonic, unlike the British Empire, will never be eclipsed.

Rod Smith, wine columnist for the Los Angeles Times, is a recipient of the James Beard Foundation Journalism Award for magazine writing about spirits, wine, and beer.