In the Lord of the Rings, Tolkien presents several dragons, which are inhabitants of Middle Earth. Their physical characteristics derive from the mythological beasts found on European legends.
The dragons were created by Morgoth in the First Age. Glaurung was an ambitious, treacherous, and compulsive liar dragon born at that Age. It is probably that Morgoth created dragons by corrupting the nature of some noble animals, through the use of his dark arts and curses.
The Dark Lord Morgoth created Ancalagon during the First Age, which turned to be the greatest and most powerful of all the dragons. Ancalagon was the first winged being able to send fire. It was so great that he was able to block the sun with his shadow, and had a hot breathing like no other. His fire breath was not powerful enough to destroy Frodo’s Ring.
Tolkien designed his own taxonomic system for the dragons, based specially on locomotion principles. Some dragons walked in four legs, like the Komodo Dragons or other reptiles. Ancalagon and Smaug were dragons able to walk and fly. The flying dragons only appeared at beginnings of the First Age; Glaurung, per example, could not do it. Those dragons not able to breathe fire were called “cold dragons”.
Another special type of dragon in Tolkien’s Literature is the Urulóki, a creature able to breathe fire. It is not entirely clear if the term “Uruloki” only talks about to the first dragons - such as Glaurung, that could breathe fire but lacked wings - or to any dragon able to breathe fire, like Smaug.
All the Tolkien dragons shared a treasure lust - especially to gold. They also possessed subtle intelligence, immense cleverness, great physical force and a hypnotic energy called “the Dragon Charm”. The best way to speak with a dragon was by not giving any direct information asked, since the dragon tended to eat any person giving a good response. But by not giving an answer at all could drive a dragon mad, which meant the death of the person keeping away the responses. Therefore, the best way to speak with a dragon was to provide half answers which lead to more questions and doubts to the dragon.
On the other hand, the Fire Dragon was able to melt many rings with its energy; four of the seven ring of the dwarves had been destroyed by the fire dragons. Nevertheless, the “One Ring” could not be destroyed by them.
Another Tolkien dragon is Scatha, displayed as a long worm, that was killed by Fram.