Isaac Asimov's Worlds of Fantasy. Book 6: Mythical Beasties

Dragon

The concept of the dragon was originally built up out of the fears of early human beings for the largest and most threatening reptiles with which they came in contact, the largest snakes and crocodiles. The very word comes from the Greek drakon, meaning a large snake.

Like the crocodile, the dragon was thick-bodied and had small legs. From the snake, some of which (though not the largest) were poisonous, it developed a fiery breath. (The poison, we can well imagine, might burn like fire when one is bitten by a snake.) Also because the snake moves unseen through the underbrush and comes upon you unaware. the notion of rapid movement, hence flight, was sometimes applied to the dragon, and it developed wings. (In the nineteenth century, scientists discovered the fossils of flying reptiles remarkably like dragons in some ways. but they had ail died out 65 million years ago and the similarity to the legend is purely coincidence.) Size, wings, fiery breath-so mighty, in imagination, did the dragons become that they began to represent elemental forces of nature, cruel and malevolent. Finally, they were viewed as the embodiment of the drive toward chaos, toward the destruction of the order built by the creative gods. In the Greek myths, the world could not be reconstructed after a universal flood till Apollo had slain a monstrous dragon called Python. (Large snakes are still called pythons today.) Similarly, in the Babylonian myths, the gods could not create the world till they had slain the dragon Tiamat. and there are rather obscure references in the Bible to God slaying Leviathan, who is pictured as the dragon of chaos.

In the/allowing story, a dragon is pictured as a personification of cold, not common in legend, and as not entirely malevolent.