The Imperator

Head of the Imperial Family. Holds all authority over any aspect of the government or military. The Head of Government and Head of State.

Powers:

Political: The Imperator solely holds the power to appoint any person to any political position in the imperium, or strip anyone from said position. Additionally the Imperator can call a general vote for an entirely new Senate, or Assembly. Or in extreme cases, the Imperator may dissolve any political body entirely.

Military: The Imperator hold ultimate authority over any military force. Able  to levy, or disband any Legion or force at any time. Appoint any person to any position, along with the rights and privileges of those positions.