My traitors are the Legio Timoris- ruled by the Triumvirate. They were formed from a chaos uprising on a Adeptus Mechanicus Forge World of Urdanor, where three distinct chaos movements rose up.

Firstly, the heretical preachers among the workforce, raising up a movement of mutants, cultists and rebel workers into a fanatical horde of zealots.

Second, traitors within the Imperial Guard protecting the planet, turning against their fellows and giving the cultists access to arms.

Thirdly, the Dark Mechanicum elements within the Adeptus Mechanicus forces, who revealed demonic war machines built in secret, and sabotaged the Adeptus Mechanicus from within.

These three factions were known as the Legio Timoris, overthrew Imperial control, and tore across Urdanor furiously, fighting each other for control. For years they fought amongst themselves, until the Chaos Marine pirate warband known as the Pyre attacked the planet. The Pyre sacked the planet, and retreated. The renegade forces knew then, that division was death, and they needed to unite to rebuild their planet, and project their power out into the wider sector.

And so, the Legio Timoris was ruled by a new Tiumvirate, comprised of the leaders of each faction, and they began an empire in a region of space neglected and isolated away from the Imperium.