St. Arnulf of Metz
Arnulf was a Frankish potentate who sought to cement his legacy among the Franks for a long time. By 605 AD, he had spent a few years in the service of King Theudebert II of Austrasia, and he came to the realization that kings came and went, but that he would most likely be remembered if he assumed a role with a rather unique title. On the other hand, Arnulf wished to show restraint in his designation, that he would not be seen as putting on airs or trying to usurp the God-given power of his king.
For this reason, some of the titles prevalent in the sixth and seventh century would not be appropriate, like "Grand Vizier", "Keeper of the Flame", or "Falconer General." It was after one of Theudebert's rowdy parties that Arnulf was tasked with the unpleasant work of asking the guests to leave, and he did it with such tact and vigor that even Salo, the King's cousin who hardly left before breakfast the next day, was headed home in a haywain by half past midnight. The next morning, the King told him, "You know what? From thenceforth I will call you the Master of the House."
It was thus that "Master of the House" became the title for the men who held the power behind the throne in the kingdoms of the Franks, and Arnulf's descendants held the title for generations hence.