Old Gods
From Twilight Wiki
The Old Gods (a.k.a. the Old Whisperings, the Elder Gods, the Old Lords or the Dread Elders) are mysterious, godlike and greatly malefic horrors which ruled in tyranny over the infant universe before they were defeated and sequestered within the primordial world of Azeroth by the Titanic Pantheon. Only very few mortals have ever been aware of the Old Gods' existence. Fewer still considered them anything more than ominous myths from a time before time began; the rumor of a dread and ancient past that should forever stay forgotten to the mortal races.
Background
The Old Gods are characterized as the sleeping evil beneath the earth, whose telepathic whispers eventually become indistinguishable from one's own maddened thoughts. Beyond the things attributed to the Old Gods as a whole, individual Old Gods share some common factors between them. Both C'Thun and Yogg-Saron are fought with a section of their bodies sticking out of the ground in the center of a room, with an unknown amount of their forms remaining invisible below. They both appear to have countless tentacles below ground, which can come to the surface to aid in combat. The battles with both Old Gods call for damage to be done to something within each Old God's submerged form to weaken or remove a shield: Killing a Flesh Tentacle in the Stomach of C'Thun and weakening the Brain of Yogg-Saron in the Mind's Eye (which may or may not represent physical places within the two Gods).
The avatars of C'Thun and Yogg-Saron, the qiraji and faceless ones respectively, are similar in a few ways. Faceless ones have similar posture and shape to qiraji gladiators (Which may be due to recycling of wireframes, to some extent). Also, both groups have a general with vaguely similar names, General Rajaxx and General Vezax, and a religious leader, The Prophet Skeram and Herald Volazj (Harbinger Skyriss too, but his affiliation is unknown).