The 'Malicious King of Medicines', as the name suggests, was an individual with a malicious heart. He was the most prestigious and famed doctor according to the rumors. He was considered 'without an equal'. However, this doctor was the most expensive in the world.
In fact, not only was the fee he charged exorbitant; there was another crucial point. One would owe him a favor if they were to seek him out for a treatment—no matter what the final result of the cure was. And one would have to return the favor whenever he wanted. As the capability of the person seeking treatment increased—the matter he'd wish them to deal with increased in difficulty.