Dudes basically a rabid dog at this point I'm surprised the King is even still supporting him
For that, if the author is smart and writes it well, it can be easily explained.
In a world of sword and sorcery, where individuals are capable of possessing superhuman powers. Think of them as living nuclear weapons. Now you know that in this world, individuals can essentially craft themselves up to become nuclear weapons. When one appears, you attempt to obtain it for yourself. Not just so that you possess the nuclear weapon, but also because if it is yours and properly controlled, you can keep it from blowing up on you. Now, of course, possessing it still puts you at risk of it blowing up.
But what's the better solution? Letting a nuclear weapon loose not knowing when it'll blow up? Having an enemy country take possession of the nuclear weapon and have the risk of it being aimed at you?
Even in the event that the nuclear weapon is the scum of the earth, if he is a scum of the earth that is easily pleased and subdued through either bribery or women. You eliminate the possibility of a nuclear explosion killing your entire kingdom by just sacrificing someone every now and then, it becomes a numbers game at that point. You could even try to go the SCP route, and you are Securing Containing and Protecting the people by containing this SCP-Hero and using D-personnel women as his harem, turning attractive female prisoners as a material for the "Maintenance" of your "Nuclear Weapon" to ensure that it doesn't accidentally detonate.
And that's going the harsh but pragmatic route of a ruler who needs to ensure the safety of his kingdom route. You can then add to that, maybe the king is foolish and does not know better. Maybe the king is ruthless and is greedy about accumulating power. Maybe the king is wise and looking towards the future and is actually actively looking to "Dismantle" high risk nuclear bombs like this Hero and is only holding unto it for now because it acts as a deterrent while trying to build up a better, more reliable nuclear weapon to replace this unsafe one.