Caesar is part of an underground race of robots, each of which start off as pieces of discarded scrap metals. These slowly get covered up with piles of dirt and trash, and gradually make their ways to the unexplored depths of the undergrounds. As these shards collect over time, they evolve and become more complex as they find new ways to attach themselves, eventually forming a coherent being. 

On a side note, these 'beings' have been known to disapprove of hat layers being used anywhere but the head.