The Overlords were created by TOG Caesar Ivanolo Buntari to act as "fixers". Caesar sees a problem and they fix it. It does not matter if the solution is an assassination or a simple word in the ear of the troublemaker. As long as an Overlord does not hideously overreact and run amok - and he is given plenty of latitude with the definition of "amok" - he acts with the power of the Caesar. Defying one is not considered an act of moral courage, it is considered insanity or suicide.
Because Overlords are so powerful, the first act of any Caesar is to sweep his predecessor's Overlords out. A few of them may already be hors de combat because of the struggle for the throne, but the rest are a threat just waiting to erupt. In the past there have been anywhere from 31 to 59 Overlords: the present count is 49.
The most powerful Overlord is the one who heads the Lictor, and he is responsible for all espionage, counter espionage, assassination and blackmail within TOG. The other Overlords are accorded status within the Lictor and often make use of Lictor agents and resources in the course of their duties. They are also able to wield power within the normal military structure above and beyond commanding their Praetorian Guard units - but that sort of appointment comes only after a direct order from the Caesar or Imperial Senate.
Overlords have been likened to pit bulls, in that once they have been assigned a task they do anything and everything they need to successfully complete it. For most of them, Overlord is the highest post they will ever achieve. They realize their power and fate are directly tied to the rule of the Caesar who so favored them, so they do what they must to insure his continued survival.