Wikipedia
Under the Merovingian dynasty, the mayor of the palace or majordomo (maior domus) was the manager of the household of the Frankish king. The office existed from the sixth century, and during the seventh it evolved into the " power behind the throne" in the northeastern kingdom of Austrasia. In 751, the mayor of the palace, Pepin the Short, orchestrated the deposition of the king, Childeric III, and was crowned in his place.
The mayor of the palace held and wielded the real and effective power to make decisions affecting the kingdom, while the kings had been reduced to performing merely ceremonial functions, which made them little more than figureheads ( rois fainéants, "do-nothing kings"). The office may be compared to that of the peshwa, shogun or prime minister, all of which have similarly been the real powers behind a ceremonial monarch.
In Austrasia, the mayoral office became hereditary in the family of the Pippinids. In 687, after victory over the western kingdom of Neustria, the Austrasian mayor, Pippin of Herstal, took the title Duke of the Franks to signify his augmented rule. His son and successor, Charles Martel, ceased bothering with the façade of a king, and the last four years of his reign (743–47) were an interregnum. See also Royal Administration of Merovingian and Carolingian Dynasties.
Usage examples of "mayor of the palace".
But in the public distress, the mayor of the palace had been compelled to apply the riches, or at least the revenues, of the bishops and abbots, to the relief of the state and the reward of the soldiers.
Once domestic tranquility was restored Jubal did not mind that his kingdom was now ruled by a mayor of the palace.