The True Overlords.
In comparison to their towering robotic forms, these guys
are tiny (barely reaching Enzo's knee)
In traditional stories, Goblins have loved treasure. The Overlords are similar, the mines contain godly amounts of valuable ore, gold, diamonds etc and they wont stop until they claim all of it for themselves. Of course, the slaves do the digging whilst the Overlords sit back and pick one of them to attack for fun. They have a habit of constantly keeping track of numbers which represents how wealthy they have become.
Behind the scenes, away from the working portions of the mines, the overlords enjoy their luxurious life away from the robotic forms such as night clubs and gambling.
I will post their robotic forms soon. It's still a work in progress as I'm not happy with the colour for the armour at the moment.