The Imperium of Man has thrived for millennia. Founded by the God-Emperor, it is threatened by aliens from without and heretics, traitors, and mutants from within. However, despite such terrible odds, the Imperium has stood strong, defended by the regiments of the Astra Militarum, better known as the Imperial Guard, the Battlefleets of the Imperial Navy, the war machines of the Adeptus Mechanicus, the Battle Sisters of the Adepta Sororitas, the agents of the Imperial Inquisition, and the Battle-Brothers of the Adeptus Astartes, better known as the Space Marines. Since the God-Emperor ascended to the Golden Throne after he was mortally wounded by Horus, the physical act of leading the Imperium is carried out by the Senatorum Imperialis, also known as the High Lords of Terra.