Exarch of Orcus
Could be the cause of the downfall of Phaervorul. Not much is known about him other than the fact that he leads drow undead and demons in the Underdark.
After his takeover of Phaervorul, he had become the lead general of the Brother-Sister dragons in Lykovia.
After the Heroes of the Portal killed him in his strong hold, Orcus tried gaining their favor as well. With this breakdown in armies, the dragon siblings were weakened.