Hive of Races

Here, he began building mechanical assistants for himself, and later, he built a city and created an army (initially for defense).

I doubt he could have done all of that alone. Perhaps he established a religious brotherhood of technocrats in the Silver Cities (something like the Hammerites order from Thief) with a philosophy along the lines of "True power and order lie in science. Technology is the next stage of our evolution." He became their messiah, and they are ready to do anything for him (even create kamikaze units like the fanatics of Nod). And in his later years, he was connected to a life support system so that he could live forever, and his consciousness was linked to the machine control system. So, in reality, he became a god – he is present in every machine, sees everything, and knows everything.
Maybe he even created a virtual paradise where the consciousness of his followers is stored (but this must be earned). And when needed, he can give them a second life in a machine body.