Machine God

The Machine God (also known as the Omnissiah or Deus Mechanicus) is a theological entity in the Warhammer 40,000 universe. It is worshipped by the Imperial scientists and engineers (known collectively as the Cult of the Machine, or Adeptus Mechanicus) as the bestower of all technology and scientific wisdom. This conflicts with the standard Imperial theology where the only God is the God-Emperor of Mankind and is actually a heresy punishable by death. But since the Adeptus Mechanicus is vital to the survival of the Imperium this issue is often avoided by simply dismissing the Machine God as an aspect of the Emperor, something the Cult itself also believes, at least officially.

There are some hints in the background stories that the Machine God may really exist, and may actually be the C'tan Void Dragon, an ancient entity of immense power. It is rumored that the Void Dragon sleeps in a stasis-tomb on Mars, the homeplanet of Adeptus Mechanicus. Were the Void Dragon to be disturbed it would probably lead to much badness for the Imperium and bring about the total victory for the necrons. Probably.