Dekang is the world's largest manufacturer of pre-mixed vaping liquids (meaning base, flavoring, and nicotine, bottled and ready-to-vape). They are way bigger than whoever is in second place, which is another Chinese company for sure, like Keemer or Hangsen.
I read some advertising blurb on a vendor site that stated that Dekang "invented" e-liquid. That's silly. Dekang didn't invent juice any more than they invented vaping. They just brought products to market before anyone else.
They make a huge line of flavored juices---fruits, candies, and hundreds of different tobacco flavors that attempt to replicate the flavor of tobacco and cigarettes from around the world. Dekang flavoring ingredients are mostly what they call "essence," which is a polite term for synthetic flavoring made in a lab. Some of their juices also use plant and food extracts.
As with any dominant company in a specific marketplace, Dekang is both the standard against which to measure, and a target for scorn. Many vapers swear by Dekang juices and love them, others swear at them and would never be caught dead vaping Dekang. Their two most popular juice flavors are probably RY4 and DK-TAB (acronym for Dekang Turkish-American Blend).
On ECF, there's considerable anti-Chinese sentiment, based largely on the argument that the Chinese are careless, producing shoddy or even toxic products and cheap knock-offs. How much of that is actually true versus silly stereotype depends on the eye of the beholder. Judging from videos on YouTube, Dekang production facilities (juice-making factories) appear to maintain very high standards of quality, cleanliness, and purity. They're all clean-room antiseptic, with high-tech air-filtering, air-lock entrances and exits, and with all the workers wearing haz-mat suits. Draw your own conclusions.
Because nicotine is a controlled substance in the U.S., most of the diluted-liquid nicotine used to make e-liquid comes primarily from two Chinese sources. Apparently it is pharmaceutical-grade and very pure. Better be, because we're all vaping it.
Because Dekang is a Chinese manufacturer, retail prices for their juices are usually much cheaper than for most U.S.-made juice. Ordered from a Chinese retail internet vendor (such as HealthCabin), the prices are extremely inexpensive except for shipping, which is higher, of course. Even from certain U.S. vendors---such as Madvapes or ValueVapor---Dekang liquids are a bargain, price-wise.
Personally, my preference is for juice from small-scale, artisan juice makers/vendors, because their juices taste better to me, but Dekang is what it is---the 800 lb. gorilla of e-liquids.