I'm not sure whether being slightly unhinged is a prerequisite for even wanting to be a king, or whether constantly having to look at the tops of people's heads as they grovel before you, permanently warps your psyche in slantendicular ways, giving you a sense of entitlement which you don't really deserve ..... not to mention underlings saying things like "Your merest whim is my command, Sire...." It does funny things to your mind, I would think - though probably no more so than being President or Prime Minister at the present time.
Once upon a time a man became king by being chosen by the High Priestess, a procedure which strikes me as eminently civilized. In more recent eras it became simply a matter of doing in all other potential candidates, "with extreme prejudice" as the saying goes, which essentially means that the strongest, most determined and most ruthless (or perhaps just the sneakiest) contender wins. Belonging to the right family (and the right religion) helped, of course. But then, having become king, you're continually glancing over your shoulder, wondering who among your courtiers is plotting to murder you .... if you're not crazy to begin with, you stand an excellent chance of going gradually bonkers in a very few years. Not many kings, emperors, czars, pharaohs or whatever, pre-19th century, died peacefully in their beds at an advanced age.
I wouldn't want the job, myself. Although as I think I might have mentioned before, I was May King for a year in our local Pagan community, having "won" the Great Wild Boar Hunt - actually, throwing wooden javelins at an image of a wild boar painted on a sheet of plywood. I didn't get to marry the High Priestess, though.....