Knickname given to a particular Drow mage turned Dragon who used to live in a city built on the ruins of Kadath. His orignal name appears to have been "Iruloki Borrese" (Ear-ew-low-key Bore-ease, spellings vary), of Clan Crying Sable Raven.
In the last days of the Elven Empire, shortly before the War of Tears, he was a researcher into experimental magics at ATAR (the Academy for Therugic Advanced Research), attached to the University of Mount Everwhite, high in the mountains of what is now the Empire of the Sun.
His area of research -- Extraction magics -- involved the ability to draw mana directly from life (living plants and beings), and may have had other aspects that are unrecorded. Concerned about the dangers and direction of his research his work was placed under and Imperial Ban, although it appears that he continued anyway, outsie of the academy and under the patronage of parties who were later to be key figures in the start of the Civil War.
Not much is known about him from the time of the War until recently. It is known that his wife, Lady Sellina, died in the War -- something that affected him deeply -- and that at some point he took on the form of an enormous humanoid dragon. He gathered followers and servants and built a city on the volcanic ruins of Kadath, surrounding and hiding the city with a hurricane force sandstorm.
So thrice ten leagues of glassy ground, With fire founts are girdled round: And here gods sang a funeral dirge, Where blossomed hate and enemies, And here they placed a ruby scourge, Concealed in crystal greenery.
The name Ruby Scourge stuck and has been used for him since.