The various figures now called dragons probably have no single origin, but were spontaneously envisioned in nearly every different culture around the world, based loosely on the appearance of a snake and/or large bird of prey and possibly fossilized dinosaur and Tertiary mammal megafauna remains.

They are commonly portrayed as serpentine or reptilian, hatching from eggs and possessing long, typically scaly, bodies; dragons are almost always portrayed as having large eyes, a feature that is the origin for the word for dragon in many cultures, and is often (but not always) portrayed with wings and a fiery breath.

Although dragons (or dragon-like creatures) occur commonly in legends around the world, different cultures have perceived them differently. Chinese dragons (Simplified Chinese: 龙; Traditional Chinese: 龍; pinyin: lóng), and Eastern dragons generally, are usually seen as benevolent, whereas European dragons are usually malevolent (there are of course exceptions to these rules). Malevolent dragons also occur in Persian mythology (see Azhi Dahaka) and other cultures.

Dragons are often held to have major spiritual significance in various religions and cultures around the world. In many Eastern and Native American cultures dragons were, and in some cultures still are, revered as representative of the primal forces of nature and the universe. They are associated with wisdom—often said to be wiser than humans—and longevity. They are commonly said to possess some form of magic or other supernatural power, and are often associated with wells, rain, and rivers. In some cultures, they are said to be capable of human speech.

Dragons are very popular characters in fantasy literature, role-playing games and video games today. The term dragoon, for infantry that move around by horse, yet still fight as foot soldiers, is derived from their early firearm, the "dragon", a wide-bore musket that spat flame when it fired, and was thus named for the mythical beast.

SYMBOLISM: In medieval symbolism, dragons were often symbolic of apostasy and treachery, but also of anger and envy, and eventually symbolised great calamity. Several heads were symbolic of decadence and oppression, and also of heresy. They also served as symbols for independence, leadership and strength. Many dragons also represent wisdom; slaying a dragon not only gave access to its treasure hoard, but meant the hero had bested the most cunning of all creatures. In some cultures, especially Chinese, or around the Himalayas, dragons are considered to represent good luck.

IN CHRISTIANITY: The Latin word for a dragon, draco (genitive: draconis), actually means snake or serpent, emphasising the European association of dragons with snakes. The Biblical identification of the Devil and the serpent thus gave a snake-like dragon connotations of evil. The demonic opponents of God, Christ, or good Christians have commonly been portrayed as dragons. In the Book of Job Chapter 41, the sea monster Leviathan, which has some dragon-like characteristics, is described as God talks about the "king of beasts" that lived upon the Earth at a former time.

In Revelation 12:3, an enormous red beast with seven heads is described, whose tail sweeps one third of the stars from heaven down to earth (held to be symbolic of the fall of the angels). In some translations, the word "dragon" is used to describe the beast,since in the original Greek the word used is drakon (δρακον).

In iconography, some Catholic saints are depicted in the act of killing a dragon. This is one of the common aspects of Saint George in Egyptian Coptic iconography, on the coat of arms of Moscow, and in English and Aragonese legend. In Italy, Saint Mercurialis, first bishop of the city of Forlì, is also depicted slaying a dragon.

IN EAST ASIA: Asian Dragons are commonly symbols of good luck/health in some parts of Asia. They are also sometimes worshipped and are considered as mythical rulers of weather and water. Dragon also symbolizes imperial authority in China.

HISTORY AND ORIGINS OF DRAGONS: Some believe that the dragon may have had a real-life counterpart from which the legends around the world arose — typically dinosaurs are mentioned as a possibility — but there is no physical evidence to support this claim, only sightings collected by cryptozoologists. In a common variation of this hypothesis, giant lizards such as Megalania are substituted for the living dinosaurs. Another less common claim is that dragons are based upon some sort of flying machines possessed by some ancient, unknown culture. Both of these hypotheses are widely considered to be pseudoscience.

Somewhat more plausibly, dinosaur fossils were once thought of as "dragon bones" — a discovery in 300 BC in Wucheng, Sichuan, China, was labeled as such by Chang Qu.[1] It is unlikely, however, that these finds alone prompted the legends of flying monsters,[2] but may have served to reinforce them.

Herodotus, often called the "father of history", visited Judea c.450 BC and wrote that he heard of caged dragons in nearby Arabia, near Petra, Jordan. Curious, he travelled to the area and found many skeletal remains of serpents and mentioned reports of flying serpents flying from Arabia into Egypt but being fought off by Ibises Histories. Histories (Greek). Retrieved on 2006-06-14.

According to Marco Polo's journals, Polo was walking through Anatolia into Persia and came upon real live flying dragons that attacked his party caravan in the desert and he reported that they were very frightening beasts that almost killed him in an attack. Polo did not write his journals down — they were dictated to his cellmate in prison, and there is much dispute over whether this writer may have invented the dragon to embellish the tale. Polo was also the first western man to descibe Chinese "dragon bones" with early writing on them. These bones were presumably either fossils (as described by Chang Qu) or the bones of other animals. It has also been suggested by proponents of catastrophism that comets or meteor showers gave rise to legends about fiery serpents in the sky. One theory proposed for why the archetype of the dragon seems to be widely present in many cultures is that it allegedly contains elements of three predators, the leopard, the snake, and the eagle.

In Greek mythology there are many snake or dragon legends, usually in which a serpent or dragon guards some treasure. A serpent dwelt, coiled up in the shield of Pallas Athene, guardian of Athens, and the first Pelasgian kings of Athens were half human, half snake. The dragon Ladon, guarded the Golden Apples of the Sun of the Hesperides, daughters of Atlas, who held the sky upon his shoulders. Another Serpentine Dragon guarded the Golden Fleece of Aetes, king of Colchis, protecting it from theft by Jason and the Argonauts. Similarly Pythia and Python, a pair of serpents guarded the temple of Gaia, and the Oracular priestess by the same name, before the Delphic Oracle was seized by Apollo and the two serpents draped around his winged caduceus, the symbol of medicine, healing and of pharmacies to this day. Zeus, in becoming king of the Gods on Mount Olympus, first had to conquer the Titans and their last defense, the serpent Typhon. The Greek stories of Zeus and Typhon, and Hercules and Ladon seem derived from Canaanite myth where Baal overcame Lawtan, and Israelite Yahweh overcame Leviathan. These stories too go back still further in history 1,500 BCE, to the Hittite or Hurrian hero Kumarbi who had to overcome the dragon Ilyukanas of the Sea. In Babylonian myth Marduk, of the same period, conquers Tiamat, the “mother of all life” portrayed as a serpentine dragon of the sea. But Marduk was only the last of a line of dragon-slaying kings of the Gods. Earlier, before Babylon was more than a tiny village, Enlil, Lord Air, of the temple of E-kur (The House of the Mountain) of the ancient Sumerian city of Nippur, became king of the Gods by slaying Tiamat by shooting the arrows of his winds down her throat, cutting up her body and making from her ribs the vault of the heavens. The weeping eyes of this salt-water goddess became the source of the Tigris and Euphrates Rivers, two of the four springs of the Garden of Eden. In Australian Aboriginal mythology, the Rainbow Serpent was a culture hero to the indigenous people in many parts of the country. Known by different names in different places, from the Waugal of the South Western Nyungar, to the Ganba of the North Central Deserts or the Wanambee of South Australia, the rainbow serpent, associated with the creation of waterholes and river courses, was to be feared and respected. Modern biologists have in fact shown that amongst the extinct giant Megafauna of Australia was a 45ft (15metre) python, Wonambi naracoortensis, which appears to have been a water-dwelling ambush predator, and may have been in part an explanation for these Australian stories.

Apart from the Australian Aboriginal tales, most dragons are associated with grain farming cultures and this fact offers another possible explanation for the existence of, and ambivalent relationships between humans and dragons. Grain farming was in pre-modern times a precarious occupation, for not only did one need to store sufficient grains to plant as seed next year, but also the harvest, which occurred in only one season, needed to be stored in such a fashion, as to give people access to sufficient carbohydrates to keep them alive for 12 months. This was overcome in traditional villages through a communal granary, but in the absence of cats, such grain storage was at risk of being attacked by rodents. A mouse or rat plague would have been the worst outcome for pre-modern people, and in the absence of cats, such infestations were deterred by putting a pair of snakes into the granary, with the Drako guarding the “golden horde” of the grain, the wealth of the whole community, from rodents and other pilferers. Early farming people, no less than earlier hunter-gatherers are dependent upon nature, the seasons and harvests for their livelihood. Serpents came to be seen as symbolic for this natural connection, powerful non-human beings, symbolic of the natural world as a whole, a world on which the whole human community depended. From being a needed part of the community, guarding its treasured grain, with the coming of cats, humankind's ambivalent feelings towards serpents reasserted itself, and dragons were pushed away into our cultural imaginations, with St George rescuing the maiden from being sacrificed to the dragon.

(Information is from Wikipedia)