Dragons

There are 2 types of dragons. European and Asian. although with the mixing of cultures in recent centuries the myths have started to influence each other.
The name dragon came into the English language around the 13th century, it was taken from the old french (dragon) which again in turn was taken from the Latin draconem (or draco) also from the Greek word δράκων, drakon, meaning huge serpent. This was used for any large serpent or sea snake not just mythological creatures.

Dragons are typically depicted as large reptiles with 2 sets of legs and bat like wings and fire breathers but this image started in the middle ages before this they where seen as giant serpents (this isn't to be mixed with a dragon-like creature with wings but only a single pair of legs which is known as a wyvern).

There are meany different myths and stories about the dragons to match the many different cultures and religions that these stories come from. But there are many types of creatures that come under the blanket name of dragon.
East Asian cultures are thought to have the oldest myths about the dragons. They where long giant serpents, most of them water deities. They where known for their great power and wisdom and seemingly endless lives. They where associated with the Chinese and Vietnamese emperors because of the power and wisdom they where suppose to hold. They are said be made up from 9 different animals, with nine sons, each with its own imagery and affiliations.  They are also seen as  the symbol of yang, representing the universe, life, existence, and growth. It is said in Vietnamese myths that the people are descended from a dragon and a fairy.

South and west Asian are roughly the same as the eastern but some are seen as protection (like on gates and clothing) and others (like the Persian dragons and other such creatures) where all malevolent. The Jewish religious text have a few mentions about dragon through out i.e. the book of Job and  Isaiah.

But it's not just Asia that has the myths of dragons, in Europe they have many tales. We get the name dragon on the Greeks but it was meant more for snakes then winged reptiles in myth form. European dragons are usually depicted as malevolent under Christianity; pre-Christian dragons, such as Y Ddraig Goch, the Red Dragon of Wales, are seen as benevolent, they are seen as huge winged reptiles that live in rivers or deep caves with armored hides and although they have wings they rarely fly. Slavic dragons are very similar although their names typically mean snake. Russian dragons are seen to have 3 heads and if all the heads aren't cut off they will grow back.
The tales of dragons have changed over the centuries and have become fixed in the fantasy, filling books and movies with these mythical creatures. They where often seen as big, greedy, mean and to be feared until the hero comes along and slays said dragon in a right of passage. Or the mystic wise figure that's a great ally that helps battle fears. Typically they where twisted to represent sin and a natural force against mankind.

There are many animals that could have sparked our ancient ancestors into believing that huge winged reptiles and snakes where alive such as crocodiles, giant snakes and even whale and dinosaur bones.

But as we come into a new age they are getting new life  with every kind of twist you could think of i.e. the elemental, fire, water ect all with magic powers and with all this new interest comes a new law for the dragon creature.