Just sit right back and you'll hear a tale.
Seriously. Buckle up, people, because ginger's got quite a story to tell.
Grown primarily in India (followed closely by China, as you might expect), ginger root is actually a rhizome, not a root. A rhizome is an underground stem that grows horizontally (instead of downwards) in a bulbous and nodular shape that sends out shoots and actual roots. But you knew that. You know what ginger looks like.
Ginger packs its punch thanks to a chemical called gingerol, which while not an imaginative name, is easier to say than (S)-5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-3-decanone. It's a volatile oil, meaning that it evaporates easily, which is why it's so fragrant. Gingerol's spicy chemical relatives include capsaicin and piperine – the compounds that put the heat in chilli peppers and black pepper.
When you cook ginger, the gingerol gets turned into a different chemical called zingerone through a reaction that breaks a bond between its carbon atoms. Zingerone is more mellow spicy-sweet than gingerol, which is why cooked ginger doesn't taste nearly as fierce as raw ginger. It's chemically related to vanillin (the chemical that gives vanilla its aroma and flavour), so closely that with a few simple chemicals you can actually turn vanillin into zingerone.
When you dry ginger (usually to grind it into a powder), the gingerol is instead turned into a chemical called shogaol (a name that comes from the Japanese word for ginger). Contrary to the milder and spicy-sweet zingerone, shogaol is twice as pungent as gingerol, so a little powdered ginger goes a long way.
As a medicinal herb, ginger has some serious cred with doctors. A randomized and controlled trial found that it can help reduce nausea and vomiting (the fancy word is "antiemetic"), usually from motion sickness, chemotherapy and pregnancy. And speaking of chemotherapy, a preliminary study published in 2010 showed that gingerol acted as an antiproliferation agent against ovarian cancer cells, killing them by disrupting their microtubules (the scaffolding inside a cell that gives it structure and allows it to replicate and spread).
In developing countries, where diarrhea from E. coli poisoning is the number one cause of death among infants, ginger is an important medicinal herb that is both readily available and effective.
The only real watch-out with ginger is that because it also has a mild anticoagulant (blood-thinning) effect, you shouldn't consume too much if you're already on a blood-thinning medication; that's one situation where too much of a good thing is totally a bad thing.
On top of these common uses, the list of folk remedies involving ginger is as long as my arm – including one that's too curious to go unmentioned: mounted regimens back in the pre-WW1 days used ginger as a horse suppository to make their steeds hold their tails high and step lively.
I suspect if someone stuck ginger up your whatnot, you'd step lively too. Wowza.