Regent of the Sith Empire was an informal title within the chain of command of the Sith Order of Decreto. A position of significant power, the Regent ruled the Empire in the Dark Lord's stead, taking over his responsibilities whilst the Emperor was away; usually at war.
Created in 61 ABY, Darth Micail was the first Regent of the Sith Empire; tasked with ensuring the smooth transaction of the conquered territories from an Alliance economy to a Sith one. As Regent, Micail had the power to change anything he saw fit, less it conflicted with the Emperor's direct commands. Following Micail's death in 75 ABY the title passed on to Darth Wyyrlok.