Who were the drones specifically in Plato's Republic Book 9?
Specifically, I do not think that the drones are any individuals in particular. Instead, they are part of the personality of a certain type of individual. The drones are the part of a person's personality that let his evil impulses rule him. When this happens, the person becomes "tyrannical."
What Plato says is that all people have bad impulses but that we have ways to master those impulses. But some people (usually because of having bad influences in their lives) stop trying to master those impulses and they come to have a "master passion" that just tells them to give in all the time. That "master passion" is the drone. Here's a quote that might help:
his father and friends take part with his moderate desires, and the opposite party assist the opposite ones. As soon as these dire magicians and tyrant-makers find that they are losing their hold on him, they contrive to implant in him a master passion, to be lord over his idle and spendthrift lusts --a sort of monstrous winged drone --that is the only image which will adequately describe him.