Malcador the Sigillite

Malcador the Sigillite was the Emperor's regent, the first Lord of Terra, and the mind that kept the Imperium running while his master chased the Crusade. He founded the Administratum, the Officio Assassinorum, and the first shapes of the Inquisition and Grey Knights.

He sat the Golden Throne so the Emperor could board the Vengeful Spirit, and the effort burned him to ash. That was the cost he had already accepted. He spent his last strength buying a few more hours of a war he knew they would not win cleanly.

Terra still runs on his paperwork. The Inquisition still argues in rooms he designed. He would have called that a kind of victory.