I doubt those kings can be killed. I think victory against them comes more from inserting layers of suppression between them and action, to modulate and reduce their power. You might be able to think of those layers as governmental machinery.
Not sure why this was downvoted - I think it's fairly well evidenced that the kings have an infinite number of clones, if they aren't actually "unkillable".
The governmental machinery analogy appeals to me as well - on the face of it, one might see this as some benevolent force of mediation and control. In reality, however, the human mind seems to function with all the bureaucratic inefficiency and politicking one would expect of an actual government.
(Since there didn't seem to be one for this month, and I just ran across a nice quote.)
A monthly thread for posting any interesting rationality-related quotes you've seen recently on the Internet, or had stored in your quotesfile for ages.