Balcephoth

Balcephoth of the felshadows is an unknown being who telepathically communicated with Vitus Darkwalker, a Gilnean warlock, and taught him the forbidden secrets of corruption. He is presumably a demon.

Balcephoth is only mentioned in the quest text for the removed worgen warlock quest Corruption (worgen). The original, pre-patch 5.0.4 version of the quest instead revolved around Immolate, and instead of claiming to have heard Balcephoth's voice in his head, Vitus Darkwalker described how he'd discovered the secrets of Immolate "from the depths of the nigh-indecipherable books of Balcephoth of the felshadows".