High Lords of Terra
Nominally, the head of the Imperium is still the Emperor of Humanity. However, since his ascension to the Golden Throne, the duty of ruling humanity has fallen to the Senatorum Imperialis - the Imperial Council of the twelve High Lords of Terra. The High Lords differ from each other in both knowledge and personalities, but in any case, the members of the Council are the leaders and representatives of the most powerful organizations in the Imperium. After the revival of Roboute Guilliman, he effectively became the ruler of the Imperium as regent of the Emperor and Lord Commander.