Empire's End by Allan Cole and Chris Bunch

At long last, we come to the end of the Sten series by Cole and Bunch, who moved on to other things for a while before finally splitting to write on their own - a pity, as they were a marvelous team. The Eternal Emperor has gone megalomaniacally mad at last, and Sten and his allies determine that they must fight a battle against overwhelming odds to unseat him from the throne. In a move reminiscent of the Caesars, the emperor has clandestinely supported the Cult of the Emperor, which claims he is a representative of the Holy Spheres, and has used his patsies in the Parliament to declare him God. He is ruthlessly suppressing dissent, and plans to send planetbuster bombs to destroy the home worlds of all who oppose him.

A direct confrontation is hopeless, so Sten and his allies - the Bhor, the Rom, the Zaginaws, and other disaffected cultures - begin a propaganda and guerilla campaign to harass and discredit the emperor. They also concentrate on finding out two key items - how does the emperor always return to life several years after being assassinated or dying of other causes, and where does the AM2 which powers the Empire come from?

The answer to these questions will determine whether they can remove the emperor permanently from the equation, and whether civilization itself can survive his absence. There is an extended middle section that answers these questions for the reader, simultaneously arriving at the same place as our heroes, by telling the story of how the Emperor, nee Kea Richards, got his start.

The only downside to this story is that it ends, and we never find out how Sten and his friends fared after Empire's end.