Why are dragons such a popular theme in fantasy and sci-fi stories?
In answer to the question, why are dragons such a popular theme in fantasy and sci-fi stories, I would have to say that dragons are essentially the imagination made manifest. It’s not just fantasy and sci-fi stories where dragons are such a prevalent fixture. It’s history itself.
Throughout all of recorded history there has always been some kind of creature that was labeled as a dragon. Some of the modern takes on dragons may not fit the same idea as to all of the creatures that have been called dragons in the past.
The first dragon that springs to mind which doesn’t fit specifically in the normal category of creatures is the Greek dragon Typhon. This creature is described as having a long serpentine body with a hundred snake heads sprouting from its shoulders with each one having fire in its eyes. It had arms as a man does, but possessed a serpent’s tail just like a snake and the torso of a man, but with the whole one hundred heads thing. Nor did it have wings, so the creature, one of the Grecian fathers of monsters, was called a dragon but it didn’t match the description of what we would call a dragon today. There were other creatures from Ancient Greek mythology that match the more modern description of dragons, but they also counted the hydra and the chimera as different dragons. Today, though, we consider those monsters as creatures of their own different nature without necessarily linking them back to dragons.
Other mythologies have similar monsters that they called dragons. The winged serpents of all Central and South American civilizations were considered dragons. The seraphim of Chrisitian mythology, those angels closest to God, were described as six winged serpents of fire which sounds like a dragon to me. Tiamat of the Mesopotamian religion was the primordial goddess of the sea and was described as a dragon (she’s even considered the goddess of evil dragons in the Dungeons and Dragons fantasy roleplaying game). There’s also the lung dragons of ancient eastern mythologies which served as gods and spirits of good luck and storms. They are literally all over the world and throughout all of history. Even the phrase “Here there be dragons” on old maps was actually shorthand for “we don’t know what’s here, and we should be afraid of the unknown”.
Basically, throughout all of time and space people have created and envisioned dragons in one way or another. Dragons can be thought of or described as anything, and you can call something a dragon even if it doesn’t match the description of a dragon and you wouldn’t be wrong to do so. Uncle Iroh in Avatar the Last Airbender was known as the Dragon of the West. Darth Vader from Star Wars is considered a dragon in the trope classification of his character archetype. Dragons can literally be anything. Even the argument about the dragons The Elder Scrolls V: Skyrim about whether or not their dragons with two wings and two legs are dragons or wyverns is absolutely nonsensical (though they are totally intelligent wyverns with breath weapons instead of stingers) because you can create whatever kind of creature you want and call it a dragon and that makes the damn thing a dragon. (Although I will die on the hill that true dragons have four legs and two wings.)
But, yes, in short dragons are imagination made manifest. They are so prevalent in fantasy, sci-fi, and any kind of fiction in general because dragons are one of those very concepts that has been caught in the heartbeat and lifeblood of the civilization we live in today.
If you’re interested in what else I have to say about dragons check out Were Dragons Real? and Do Dragons Exist?.