Darkwhisper

The Darkwhisper were a sect of cultists loyal to N'Zoth, led by Dark Inquisitor Xanesh and commanded by Vexiona. They infiltrated Blackwing Descent and repurposed its laboratories to conduct experiments on twilight dragons, feeding the failures to a spawn of Shad'har the Insatiable. Vexiona reveals their assault as a ruse to capture Wrathion and use his essence to raise his siblings Onyxia and Nefarian as servants of N'Zoth, though their plot is ultimately foiled by Wrathion and his companion.

Speculation
Given their name, it is likely they originated from Darkwhisper Gorge, perhaps as remnants of the Twilight Hammer forces that once resided there.