Short answers, pulled from the story.
The word dragon entered English in the early 13th century from Old French dragon, which came from Latin draco (meaning "huge serpent, dragon"), which in turn derived from the Greek drakōn. The Greek word most likely came from the verb dérkomai, meaning "I see," and is thought to have referred to something with a deadly glance or unusually sharp eyes.
Anthropologist David E. Jones argues in An Instinct for Dragons (2000) that humans inherited instinctive fear responses toward snakes, large cats, and birds of prey, and that dragons represent a composite of these ancient predator threats. Adrienne Mayor separately proposed that fossil discoveries of large prehistoric animals inspired some dragon legends in ancient Greece, India, and China. Robert Blust offered a third hypothesis: that dragons emerged from pre-scientific attempts to explain natural phenomena such as rainfall, drought, and the rainbow.
From the Han dynasty onward, the dragon became the emblem of imperial power in China. Emperors gradually became identified with dragons and claimed to be their incarnations. Eventually, only the emperor was permitted to display dragon imagery on clothing, houses, or personal articles, and any commoner possessing such items could be ordered executed. This restriction ended after the last Chinese emperor was overthrown in 1911.
The most famous version of the Saint George legend, recorded in the thirteenth-century Golden Legend, is set in the town of Silene in Libya. A dragon had eaten the town's sheep and then its children, offered as daily sacrifices. When the king's daughter was chained to a rock to be eaten, Saint George arrived, wounded the dragon with his lance, subdued it using the sign of the cross, and led it into town on a leash made from the princess's girdle. He killed it with his sword after the townspeople agreed to convert to Christianity. The first full written account of the story comes from an eleventh-century Georgian text.
East Asian dragons, including Chinese and Korean varieties, were primarily benevolent beings associated with water, rain, and good fortune, and served as emblems of imperial and royal power. Western European dragons, shaped by biblical identification with Satan and Greco-Roman serpent myths, were fire-breathing embodiments of evil associated with death, greed, and sin. The contrast is fundamental: in China, drought was blamed on a dragon's laziness; in medieval Europe, the dragon was a creature to be slain by a saint or hero.
Smaug is the dragon in J. R. R. Tolkien's novel The Hobbit, and is described as one of the most iconic modern dragons. Other prominent literary dragons include those in Anne McCaffrey's Dragonriders of Pern, Ursula K. Le Guin's Earthsea Cycle, and George R. R. Martin's A Song of Ice and Fire series.