- The Void Dragon's Hidden Identity
What I'd really like to control is not machines, but people.
Mag'ladroth, more commonly called the Void Dragon or more controversially as the Omnissiah is one of the main C'tan along with the Deceiver and the Nightbringer. The Void Dragon is more commonly associated with technology and science and thus is often the topic of various theories. The Void Dragon is a C'tan, and is hinted to be slumbering on Mars, since several sources mention The Dragon of Mars. Whether this is 100% true or just plain heresy is one of the intriguing theories as his connection with technology and the connection towards the machine worship being prevalent with the Adeptus Mechanicus is profound; and if factually true would fuck up the entire ideological construct of the IoM. Another theory is the meaning of the Omnissiah. Here it gets a bit complicated, well it may be true that the Emperor did have contact with the Void Dragon before bitch slapping him back on Mars, the notion on whether the Omnissiah is related to either the Void Dragon or Empy is up for speculation as certain clues may imply that what the Mechanicus worships is not the Void Dragon but another name for the Emperor and that the Void Dragon is constantly checked by the Emperor even when he is turned into a gold encrusted potato.
However what can be accepted is that if the Void Dragon fully awakens he will not only butt fuck the entire Imperium but also the Necrons for pulling such treachery during the War in Heaven and even Chaos once he gets his mojo running as his ability to control almost all forms of technology and machines means that he would give Chaos scrapcode a run for its money. To put how terrifying this bastard is into perspective: the the Deceiver aka the C'Tan who was unafraid of talking to psychos like the Nightbringer and the Outsider and convincing them that cannibalism was a spiffy idea, ACTIVELY AVOIDED MAG'LADROTH.
On a more hilarious note, for some reason, it can talk to human children, like Gamera, and sometimes involuntarily gives them power to heal and manipulate machinery like him. Soooo...the Void Dragon might secretly be in fact be the guardian of children all along? Just picturing a cosmic being from beyond conventional science having a soft spot for kids would generate much lulz and pedophile jokes on /tg/.
On the Tabletop
If you want to play him in an army, simply buy a Balrog or a Daemon Prince (make sure to give the latter wings), paint it suitably black, silver and green, and use it as a Transcendent C'tan. Have fun.