Dragons

Excerpt from Wikipedia article on Dragons
The association of the serpent with a monstrous opponent overcome by a heroic deity has its roots in the mythology of the Ancient Near East, including Canaanite (Hebrew, Ugaritic), Hittite and Mesopotamian. The Chaoskampf motif entered Greek mythology and ultimately Christian mythology, although the serpent motif may already be part of prehistoric Indo-European mythology as well, based on comparative evidence of Indic and Germanic material. It has been speculated that accounts of spitting cobras may be the origin of the myths of fire-breathing dragons.[2]

Although dragons occur in many legends around the world, different cultures have varying stories about monsters that have been grouped together under the dragon label. Some dragons are said to breathe fire or to be poisonous, such as in the Old English poem Beowulf.[3] They are commonly portrayed as serpentine or reptilian, hatching from eggs and possessing typically scaly or feathered bodies. They are sometimes portrayed as hoarding treasure. Some myths portray them with a row of dorsal spines. European dragons are more often winged, while Chinese dragons resemble large snakes. Dragons can have a variable number of legs: none, two, four, or more when it comes to early European literature.

Dragons are often held to have major spiritual significance in various religions and cultures around the world. In many Asian cultures dragons were, and in some cultures still are, revered as representative of the primal forces of nature, religion 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 also said to be capable of human speech. In some traditions dragons are said to have taught humans to talk.

Narratives about dragons often involve them being killed by a hero. This topos can be traced to the Chaoskampf of the mythology of the Ancient Near East (e.g. Hadad vs. Yam, Marduk vs. Tiamat, Teshub vs. Illuyanka, etc.; the Biblical Leviathan presumably reflects a corresponding opponent of an early version of Yahweh). The motif is continued in Greek Apollo, and the early Christian narratives about Archangel Michael and Saint George. The slaying of Vrtra by Indra in the Rigveda also belongs in this category. The theme survives into medieval legend and folklore, with dragon slayers such as Beowulf, Sigurd, Tristan, Margaret the Virgin, Heinrich von Winkelried, Dobrynya Nikitich, Skuba Dratewka/Krakus. In Biblical myth, the archetype is alluded to in the descendants of Adam crushing the head of the Serpent, and in Christian mythology, this was interpreted as corresponding to Christ as the "New Adam" crushing the Devil.

The blood of a slain dragon is depicted as either beneficent or as poisonous in medieval legend and literary fiction. In German legend, dragon blood has the power to render invincible skin or armor bathed in it, as is the case with Siegfried's skin or Ortnit's armor. In the Slavic myth, the Earth refuses it as it is so vile that Mother Earth wishes not to have it within her womb, and it remains above ground for all eternity. The blood of the dragon in Beowulf has acidic qualities, allowing it to seep through iron. Heinrich von Winkelried dies after the blood of the dragon slain by him accidentally drips on him.

Excerpt from Dragon Age Wiki
Archdemons are the Old Gods manifested in the form of powerful and terrifying dragons and tainted by darkspawn. They possess an intelligence far beyond the average dragon and are purely evil creatures. Most of the time, the darkspawn are organized as a simple hive-mind, concerned only with expanding the horde. They rarely appear on the surface, except in raids and small invasions.

A Blight begins when the darkspawn find and taint an Old God, who then unites them into a great horde and unleashes them onto the surface in a wave of darkness and destruction. The Archdemon is their leader, and a Blight will not end until the Archdemon is destroyed.

Before the events of Dragon Age: Origins, there had been four previous Blights, led by the Archdemons Dumat, Zazikel, Toth and Andoral, respectively.

Since the dwarves managed to fend off the darkspawn invasion of the Deep Roads after the First Blight, no Archdemon has led a Blight against them. Instead, the dwarves consider the Blight to be something of a respite, as all darkspawn activity is focused on the surface.

Resources
Wikipedia article on Dragons

Image from How to Train Your Dragon (2010)

Dragon Age Wiki: Archdemon

Dragon Age Origins: Review