Dragon

Dragons are, in the Real World at least, mythical beasts with highly variable characteristics, but usually reptilian, winged, and fond of collecting treasure. They frequently breathe fire, and often they are intelligent. In European tradition they are usually Evil or at least not kindly disposed to people, whereas in Asia they tend to be more wise guardian-type figures.

Dragons are commonly found in many different fantasy Continua:

Lord of the Rings
Dragons in Lord of the Rings are very much dragons of the European style, sometimes capable of speech, sometimes winged and sometimes not, but all evil. Many of them are fire-breathers, and the species was created by Morgoth, the first Dark Lord. Dragon-fire is one of the few things capable of melting Rings of Power, except for the One Ring; this information may be of use when dealing with Extra Rings of Power.

Dragonriders of Pern
Pernese dragons are telepathic, teleportation-capable sentient animals, genetically engineered from fire-lizards in order to be an aerial defence force against the microorganism Thread. They bond telepathically with a Human at hatching. Notably, while technically fire-breathing, this species has to chew a phosphate-bearing rock in order to actually generate fire. More detail may be found in the main article.

Harry Potter
In the Harry Potter-verse, dragons are a magical animal, extremely dangerous, but not sapient or sentient.

The Inheritance Cycle
Probably stolen from one of the above.

Temeraire
In the Temeraire series, dragons are found across the Earth, and have been since antiquity. During the Napoleonic Wars (when the books are set) they are used for aerial combat in Europe; while they are partnered with captains and crews, these partnerings are not set in stone as with Pernese dragons, and in some places (i.e. China), dragons do not choose their captains until they are several years old.