The Imperium of Man is a many millennia old interstellar empire spanning through the whole Milky Way, incorporating millions of planets, maintaining an enormous bureaucracy with countless sub-divisions, and a galaxy-wide military force. 

The ruler of the Imperium of Man is His Divine Majesty, the God-Emperor, undisputed Master of Mankind, yet he is unable to govern the Imperium in his current state bound to the Golden Throne, therefore the day-to-day rule is carried out by the High Lords of Terra, also known as the Senatorum Imperialis. 

The edifice known as the Imperium of Man is an enormous, complex structure, but an Inquisitor bearing the Rosette of the Holy Ordos stands all above these, and can requisite assistance from any of these forces, yet not all Inquisitors choose to do so, many prefer to work under cover, revealing their office only in the very last minute, or not even after that.