Void Dragon

Little is known if this is truly a C'tan, if anything substantial at all, although dark technology, machines or knowledge seem like potential speculation. It is arguably the most powerful C'tan, particularly after the banishment of the Nightbringer's "scythe" to the Warp by the Old Ones/Eldar, although The Nightbringer seems to have had a much nore sinister effect on the galaxy as a whole. The Void Dragon is widely whispered to be slumbering somewhere, in some form, beneath the surface of Mars. If what the Adeptus Mechanicus worships is truly this sinister xeno god, there is no telling what the ramifications of this discovery could be. While speculation at best, the Necron's Codex lends significant credence to the idea that the Void Dragon is on Mars (likely in the Noctis Labrynthus). The Codex mentions the suicide rush by 5 Shroud-class light cruisers that succeeded in penetrating the defenses of Mars and then landing on the planet near said location. In addition, a small inset story in the Codex mentiosn that Warmaster Abaddon and one of his lieutenants have discovered, through the spirits of the Warp, that there is a "New Kind of Death" walking Mars. While the article does not mention the Void Dragon by name, it is pertinent given the fact that it provides signifcant evidence as to the possible location of one of the final two sleeping C'tan.

References

Chambers, Andy; Haines, Pete, McNeill, Graham, and Hoare, Andy (2002). Codex: Necrons, 3rd Edition, Nottingham: Games Workshop. ISBN 1-84154-190-7.