Mephisto of the Void, also known as, G'horolox, and Vorous the Invincible, was a powerful dark spirit from the Void that acted as a speaker and figurehead for the elusive and powerful forces of Chaos during the "Season of Chaos" of 2166 C.E..
Like most other Chaos beings, Mephisto first came into being in the Warp (Void) in the Creation Era where he likely was originally a powerful neutral spirit corrupted by Y'shaarj's foulness. He is classified as an Elder of the Void. He was apparently present during several of Chaos' incursions into Creation, such as in the Hundred Years War ( 2.9 Mil B.M.), where Alicorn Empire and the Forerunner Empire fell to corruption and bloodshed. He is believed to have returned to the Void where he awaited for millennia on end, until the Season of Chaos in the 22nd Century C.E..
Mephisto was a proud and brash being, seeing himself as the voice and herald The Void and all Chaos. He saw himself as a higher being than the creatures of Existence, even higher than the Gods themselves.