system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] What was Vader's official role in the Imperial Military? Supreme Commander? Special Agent? The Emperor's Special Friend?

Basically, why did this dude officially have the legal authority to call up any number of troops or equipment, run any operation he desired, and kill anyone that displease him; obviously he could do this as Sidious's apprentice,  but what was the excuse the Emperor gave to the military?
gpt
He is the Emperor's emissary.  This is addressed in the recent comic series, after Vader became active, he found it difficult to execute the emperors commands with no military rank or authority, nobody knew who the hell he was.  At this time he discovered a plot by a group of senior officers to assassinate him.  He brought this to the emperors attention, and the emperor convened the senior officers to introduce Vader.  He was not given a military rank, the emperor simply said "This is Lord Vader, we speak as one voice, an order from him is an order from me."  And Vader, in a display of power, force choked some of the random officers.  So he really is just the emperors special friend.