Prior to its corruption by red lyrium, this creature was a high dragon of unknown origin.
The red lyrium dragon was first encountered by the Inquisition along with Corypheus at the village of Haven during his assault and attempt to regain the Anchor from the Herald of Andraste. It is initially presumed that the dragon is an archdemon, and that it brings the possibility of a new Blight, spreading fear across Thedas.
The dragon is also summoned by Livius Erimond to aid him during the Inquisition's siege of Adamant Fortress. When Warden-Commander Clarel turns against Erimond and has him at her mercy, the dragon swoops down and mauls her before tossing her aside. Before the beast can attack the Inquisitor, Hawke, their Warden ally (either Stroud, Alistair or Loghain), and their party, however, Clarel casts one last spell with her dying breath, striking the dragon's underbelly, causing it to collapse and weaken the walkway under their feet. The dragon then flees the area while the Inquisitor disappears into the Fade.
During the Inquisition's assault on the Temple of Mythal, Corypheus summons his dragon again to attack the Inquisitor and Morrigan, but they manage to evade it and escape into the magically warded structures of the temple.
Whether the Inquisitor or Morrigan drinks from the Well of Sorrows, the Well will reveal that Corypheus' dragon is not a true archdemon, but merely a facsimile of one made by corrupting an ordinary high dragon with red lyrium in which the magister invested his power. If the dragon is killed, then Corypheus' ability to leap into other bodies would be disrupted.During the final confrontation, the dragon attempts to pounce at the Inquisitor, only to be tackled out of the way by another dragon (either the Guardian of Mythal or a transformed Morrigan)The two dragons engage in an aerial battle before Corypheus' dragon manages to defeat its opponent. The Inquisitor then finishes the weakened dragon off, before taking on its master.