A greatwyrm is a type of dragon that was blessed by the Dragon King Bahamut with divine power.
Origin
It is said that when an ancient dragon amasses a large enough hoard, their power grows so immense that even the Dragon King Bahamut takes notice. Bahamut, taking on one of his many other forms, will then appear before the ancient dragon and challenge them for their hoard. If the ancient dragon loses to Bahamut, they are killed and reborn as a wyrmling, granting them another life in honor of their accomplishments. But if the ancient dragon is able to defeat Bahamut and keep their hoard, the Dragon King offers them a final treasure to add to their hoard. This treasure is a shard of his power, and accepting the gift transforms the ancient dragon into a greatwyrm.
Throughout history, a handful of other dragons have become greatwyrms through other means. Some have achieved divinity by being revered as a god by others, to the point that Bahamut himself comes to recognize the dragon as an equal. Others were blessed by Bahamut in their final moments, often due to the individual committing an act of great personal sacrifice.
Cultural Significance
The greatwyrms are viewed as a halfway point between the mortal dragons of the Inner Planes and the Dragon Gods. While not outright gods themselves, draconic culture often bestows upon them a level of cultural importance that is on par with how other cultures view gods.
According to legend, in the final years before The Blight, the greatwyrms ushered the dragons into a parallel plane to wait out the catastrophe to come. Since then, greatwyrms have become synonymous with ill omens in other cultures, as seeing one likely means that a catastrophe is near. Their absence from the Prime Material, some say, should be seen as a reassuring sign, though their absence might carry its own dangers.
