Dragons are, naturally, a fixture of the fantasy genre. But, as with all fantasy tropes, Martin has his own specific rules when it comes to his dragons. The dragons of A Song of Ice and Fire aren't big on hoarding gold or kidnapping princesses. They can't speak in the voice of Benedict Cumberbatch. Nor are they simple, dumb, flying dinosaurs, either: dragons seem connected to their people, much like the Starks and their direwolves. Dragons seem connected, in some strange way, to all that zombie nonsense going on up North. Dragons are the fire part of the whole "ice and fire" balancing act, which seems to have been thrown way out of whack. And ever since dragons have returned to the lands of Westeros and Essos, the magic levels all across the globe have been cranked up to eleven.
So here's a brief on how those big fire lizards work in A Song of Ice and Fire, and why you should never cross an angry Targaryen:
There are a lot of stories about where exactly dragons came from in the Song of Ice and Fire universe. The Valyrians claim that they discovered dragons chilling in some volcanoes over in ancient Valyria. People in Qarth say that dragons came from the moon, while other folks in Essos believe they came from eastern Asshai by the Shadow, Melisandre's creepy hometown. Some of the more scientific maesters think that dragons were created out of innocent lil' wyvern lizards using magic and selective breeding.
Wherever dragons came from, though, what's for sure is that the Ancient Valyrians went in on raising dragons to be weapons of war. They trained dragons, using them to conquer a vast empire in Essos. They had dragon horns and dragon riders and a whole terrifying dragon-based culture, until Valyria totally blew up for some unspecified reason in the Doom of Valyria, obliterating the Valyrians and their faithful lizards friends.
Except for the House of Targaryen, a family who had peaced out of Valyria 12 years ago with all their money and five dragons, following a prophecy that Valyria was about to blow. The Targaryens then used their remaining dragons to conquer Westeros, because why not? But after years of Targaryen rule and civil war, all the dragons eventually died out, leaving behind a few eggs and some creepy skeletons.
The Targaryens tried for years to hatch those dragons eggs so they could be cool dragon riders again instead of irritating blonde bureaucrats, to no avail. One attempt actually got most of the Targaryens killed in a huge fire at Summerhall, proving once and for all that Targaryens are not fire-proof. So dragons were gone for years, and without dragons, the summers became increasingly short, and the winters increasingly long.
As we all know, though, lil' Dany finally did manage to hatch three dragon eggs. It seems like the combo of the red comet overhead, the funeral pyre, the human sacrifice of the witch Mirri Maz Duur, and Dany deciding to go fire-walking somehow unlocked the right conditions for baby dragon birth. We still don't know exactly why it worked, but it seems clear that dragons require some sort of fiery blood-magic sacrifice to get them started.
And now that there are dragons back in the world, magic seems stronger all over the place. Melisandre can suddenly have creepy shadow babies. The White Walkers are approaching. The weird glass candles at the Citadel are burning. And Dany's babies are getting bigger. Dragons will grow indefinitely if allowed to roam free, hence when Drogon has grown huge while off eating sheep and small children, but Viserion and Rhaegal are slightly smaller after being imprisoned in Meereen. They can all fly and breathe fire just fine, though. And according to the maesters, dragons have no fixed sex or gender, meaning that any of Dany's dragons could conceivably be the mother of more dragons.
The trouble is that Dany, being a cool young teen, is not so great at setting boundaries for her kids. Dragons will bond with one dragon rider, but she has three little monsters to take care off. One person can't ride more than one dragon. And as much as the Targaryens like to talk up being Targaryens, having Targaryen blood doesn't necessarily mean that dragons like you. It seems to help a little, but the bloodlines certainly don't have to be "pure." Targaryen bastards have successfully ridden dragons throughout the history of Westeros.
Targaryen or not, Dany is going to have to find another two dragon riders if she wants to keep all three dragons on her side. Many fans have speculated that Jon Snow will end up with one of them and that the other will fall into less heroic hands (or perhaps even end up as a zombie dragon).
But the real mystery here is how the dragons seem to affect the world around them. We know that for the most part, dragons work like intelligent animals: they bond with people, they eat (cooked) food, they lay eggs. But they also clearly have some kind of affect on the season, and on magic all across the various realms. Could bringing dragons back in full force be the way to stop the White Walkers and get those wacky seasons back on track? Or will things only settle down once both White Walkers and dragons are completely gone? Can ice monsters and fire lizards live in harmony? Did the whole weird, extra long season things start when dragons appeared on the planet, or are they the ones who've been keeping the seasons in check?
Let's hope that the next book holds some answers for our scaly, leather-winged friends.