Setherien the Black Drake was the greatest threat faced by the Descendant races in Anthos. Under him, the Druid Grove was corrupted and tainted, as was the Malinorian city of Luminaire and Lenfarthing, home of the Halflings. Abresi, capital of Oren, was largely destroyed by one of his attacks.
Not much is known about how Setherien came to be a Drakaar, but we do know that he was once an ordinary drake that terrorized Kal'Karik with his mate when the Dwarves dug too deeply in the ruined city. After destroying the Dwarves there, he left and not much is known of what happened after, until he invaded the island known now as Burzumkutotaz. In Burzumkutotaz, Setherien corrupted the native villagers with his fire, forcing them to serve his cause. When a holy order known as the Order of the Golden Lance came hunting after him, he corrupted them as well, turning them into the Harbingers, powerful creatures imbued with his power to corrupt.
When the Descendants came to Anthos, Setherien had just begun the process of invading the vast North. He had started to corrupt the native Bohra tribes that lived there, and in return they had been starting to attack the Descendants in the North, fleeing from the coming threat. It slowly became apparent that there was something else in the North, and expeditions were sent up, but most of them never returned. When all the Bohra were corrupted to Setherien's cause, he began his invasion. First he took the fortress known as Greywyn and corrupted it with vast gouts of flame, renaming it Urkvorkuhz Gul. He and his Harbingers then tainted the Druid Grove in Malinor and began raiding surrounding settlements repeatedly.
With a combined force of Descendants led by the Orcs, Greywyn was retaken and destroyed. The black Drake then destroyed Luminaire, which was never rebuilt. Abresi was also attacked, and a good three quarters of it was razed to the ground. His greatest defilement, though, was corrupting the old Cloud Temple on the West coast of Anthos. The Monks were forced to move to the center of Anthos, where they were better protected.
Setherien was finally defeated in the Fringe when the Order of the Golden Lance destroyed him with the Golden Lance of Xan. His Harbingers became mortal beings once more, and lost all their magic granted to them.
Setherien was a Drakaar, which mean he could take two different forms. His first form was that of a human warrior, hooded with red eyes.
He rarely used this form, and almost nobody saw him in this form. His other, more common form, was that of a massive black drake.
The corrupting fire, which he used to bend mortals to his will. It is unknown if anybody could resist him when he used this.
Massive strength - he once was eaten by a Shurr'dru and destroyed it from the inside
Invincible to conventional weapons