"Prelude to Foundation" by Isaac Asimov.

Prelude to Foundation Prelude to Foundation is the beginning of a great series of science fiction books by Isaac Asimov. It is the year 12,020 G.E., and Emperor Cleon I sits uneasily on the Imperial throne of Trantor. Here in the great capital of the Galactic Empire, forty billion people have created a civilization of unimaginable technological and cultural complexity. Yet Cleon knows that there are people who have the desire to see him fall, …

…by the Imperial army. The book ends with Hummin coming and telling Seldon that all along he was Demerzel and that he was actually the only robot left from Earth. Robots were destroyed 20,000 years ago when they started a war against humanity. He was a traitor, now under disguise of Demerzel. He explains to Seldon why the Empire is dying and what he should do next. The next book in the series is the Foundation.