I'm posting this on Mangadex, a place mostly about posting and scanlating mangas so it's not my original sadly xD But imma keep pilot beause I think that works well
Master, because it fit for a golem and being controled by the inside or by external spells don't change that. But it depend. For me, controler, manipulator, pilot, operator, handler and others terms like that sounds more like "engineering" than magic and old medieval-fantasy. It totally depend of the setting used by the manga you want to traduce, for this golem specificaly. If the golem is kind of like a mecha, master is not right and other previous terms are the way to go. If it feel like magic control, spells and so on, master should be better.