To Tolkien, dragons were the greatest and most magnificent works of the Enemy, embodying pure malice, wickedness, elemental strength, and terrifying power.
Tolkien's dragons have, like everything else in Middle-Earth, a long and detailed history. They were created from fire and sorcery in the First Age of Sun by Morgoth in his fortress of Angband. Divided first into those that crawled like snakes, those that walked on four legs, and those that flew on bat wings, and second into the Uruloki or Fire-Drakes and the Cold-Drakes, all shared these attributes in common.
First, all the dragons were terrifyingly huge and strong, with lethal teeth and claws and almost impenetrable scales. Second, their senses were sharper than any other creatures (remember the encounters between Smaug and Bilbo?). Third, they were immensely clever and knowledgable, with a great love of riddles and and puzzles, a power marred only by their flaws of pride, greed, gluttony, and wrath. Lastly, they exerted hypnotic power over lesser creatures, able to bend others to their overpowering will with a gaze and a few whispered words.
Some noteworthy dragons:
deserves his own writeup. In brief: four legs, wingless, first of the Uruloki, Father of Dragons, devastated the armies of the Elves
in the Dagor Bragollach
and Nirnaeth Arnoediad
, sacked and occupied Nargothrond
, finally killed by Turin Turambar
Ancalagon the Black
Mightiest of all the dragons of Middle-Earth, he devastated the armies of the West in the War of Wrath
. Finally killed by Earendil
and cast down on the towers of Thangorodrim
, which were broken by his fall. His name means "Rushing Jaws".
Smaug the Golden
The greatest dragon of the Third Age. A winged Uruloki who destroyed the city of Dale and took over the Dwarven citadel of Erebor in the year 2770, occupying it for 200 years until slain by Bard of Esgaroth.