Emperor of the Terran Imperium

Contrary to public imagination and imperial propaganda, the emperor of the Terran Imperium was not in any way an absolute monarch. In most cases, the emperor was a figurehead, albeit one with an incredibly impressive mouthpiece. On paper, the Terran Imperium was an elected constitutional monarchy, but rarely functioned as one.
 

Legal Powers

The only areas where the emperor had direct authority were over the Imperial Palace complex, the Imperial Guard, and the command ships Imperium and Imperious. The command ship Imperator was considered a fleet vessel and therefore fell under the authority of the Admiralty, but was placed at the disposal of the emperor.      

Military Authority

While the commander in chief of all armed forces, the emperor would only have strategic command authority. All other matters, such as design, tactics, logistics, and staffing were handled by the Military Consul. In most cases the Admiralty and Design Board would consult with the emperor regarding new designs. As with other high government offices, the emperor could appoint officers to the Admiralty or name a Grand Admiral, with the confirmation of the Convention of Houses.      

Government Authority

The emperor had the ability to appoint the Prime Minister and the three government Consuls, but all had to be confirmed by the Convention of Houses. Once installed, the emperor could only suspend these officials, and could not remove them directly. The emperor also had the ability to classify or quarantine any document at any time, for any reason. The most widely used power of the emperor was their veto power, whereby the emperor could veto any government decision, at any level.
  The Prime Minister was required to keep the emperor fully informed of all government business, and the emperor had the right to meet with any government minister directly when needed. The extent of this personal involvment would vary from emperor to emperor.      

Judicial Authority

Only the emperor could pass a death sentence with the recommendation of the judiciary. In addition, the emperor could offer clemency, but only after a conviction.      

Imperial Edicts

Imperial edicts held the force of law but required the consent of the Prime Minister and the relevant Consul, and could be overturned if needed by the Convention of Houses or the Convention of Worlds.      

Lord Protector of Jerusalem

In 2103 Emperor Gerard II would conclude the negotiations for the Treaty of Jerusalem, the terms of which removed the Old City of Jerusalem from both Israeli and Palestinian control by placing it under the direct authority of the emperor as an imperially managed territory. As part of this arrangement, the emperor would become Lord Protector of Jerusalem.      

Succession

The emperor of the Terran Imperium was technically an elected official. Upon completion of their coronation and enthronement ceremonies, the emperor would name their Prime Minister. Once confirmed, the Prime Minister was the heir to the throne. When the emperor died, the Prime Minister would be confirmed by the Convention of Houses as the emperor and would then be allowed to take the throne. While the Convention of Houses had the power to deny the succession, this was a power it would never exercise, exacerbating the Imperial Succession Crisis.
  It was possible for a Prime Minister to decline the throne, or for it to be declared at the time of their appointment that it was for a limited time. For a period of 3 days after the coronation, the emperor had the ability to dismiss and reassign any high government officials.      

Combined Powers

In the absence of a Prime Minister, the emperor would assume the duties and powers of the Prime Minister in addition to their own. A number of emperors would deliberately delay naming a Prime Minister for this very reason, as doing so gave them the power to rule as near absolute monarchs. However, doing so came with risks. Emperor Gerard V acted as his own Prime Minister, allowing Claudius Carruthers to assassinate him without a designated heir to contend with.      

Taking the Throne

Becoming emperor required two separate ceremonies, each granting different powers and authorities.    

Enthronement

The enthronement ceremony would typically come first, where the new emperor was invested with the right to wear the silver imperial pauldrons, silver uniform insignia, and carry the imperial sword as a symbol of their authority over the Imperial Guard. The ceremony itself was very simple, with the new emperor being announced, entering the throne room, and standing before the throne. Their confirmation of election by the Convention of Houses would be read aloud, and the new emperor would then sit on the throne. Upon completion of the enthronement, the emperor would have the common imperial powers over the palace and Imperial Guard.  

Coronation

From the reign of Alexander I onwards, all imperial coronations were held in the Hagia Sofia in Constantinople. The new emperor would approach the altar barefoot, wearing a distinctive white imperial uniform, where he would receive the blessings of the Pope, Patriarch of Constantinople, Patriarch of Moscow, Archbishop of Canterbury, the senior rabbi of Jerusalem, the Imam of Mecca, the Dalai Lama, the chief priest or priestess of Ise Shrine, as well as several chiefs of Native American and African tribes.  Others would occasionally be added from other regions of Terra or species residing in the imperium.  This process could take several hours to complete.
  After receiving these blessings, the emperor would be dressed in gilded pauldrons, imperial purple cloak, and golden uniform insignia. Finally, the golden coronation crown would be presented, and the gathered officials would read the emperor’s new throne name and initial imperial titles. These titles included “Lord Protector of Jerusalem,” “king of kings,” and a variation of “emperor of the Terran Imperium.” Upon receiving the full title, the crown would be placed on their head, and the emperor would step out to the plaza to be announced to the people using their full title and name.
  Only after completing the full coronation would the emperor have their full powers as listed under the Imperial Charter.      

Regency

It was initially thought that the Prime Minister could take up the duties of the emperor for a short time if needed, and no provision was provided in the Imperial Charter for a regent. As the Imperium grew and became increasingly complex, however, it was felt that such an office would be needed, and efforts were made to clarify the position. This would ultimately never be done, in spite of the number of emperors serving as their own Prime Minister. When Prince Constantius was named Prince Regent for Theodosius IV, a number of issues had to be resolved by the Convention of Houses on the spot. Certain powers were withheld, such as the right to issue Imperial Edicts or to suspend government officials.      

Lictors

From the reign of Traian onwards, all emperors would be accompanied to official functions by palace appointed Lictors, two of which would carry fasces in the Roman tradition. Most emperors would add an additional Lictor as a note taker. Claudius would have additional Lictors carrying flails that he would threaten to use on any official who displeased him.      

Regalia

The full imperial regalia would vary from reign to reign, but always included the gilded pauldrons, imperial cloak, imperial sword, and the coronation crown. Usage of the regalia would also vary, with most emperors opting not to wear the crown except for their coronation and leaving out the imperial cloak. Other emperors would add items, such as Claudius including a crook and flail. 
  The first two Rauschning emperors only wore the imperial regalia during their enthronement and coronation ceremonies.  Constantius would wear the military uniform with gilded pauldrons daily until the end of the Monsos War, at which point he wore them only on formal occasions as other emperors did.