After the reign of Dagobert I (629–639) the Merovingians effectively ceded power to the Pippinid Mayors of the Palace, who ruled the Frankish realm of Austrasia in all but name. They controlled the royal treasury, dispensed patronage, and granted land and privileges in the name of the figurehead king.
Source: Charles Martel – Wikipedia
Under the Merovingian dynasty, the mayor of the palace (Latin: maior palatii) 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”).
Source: Mayor of the Palace (Wikipedia)
Tim B.
“There was nothing left the King to do but to be content with his name of King, his flowing hair, and long beard, to sit on his throne and play the ruler, to give ear to the ambassadors that came from all quarters, and to dismiss them, as if on his own responsibility, in words that were, in fact, suggested to him, or even imposed upon him. He had nothing that he could call his own beyond this vain title of King and the precarious support allowed by the Mayor of the Palace in his discretion, except a single country seat, that brought him but a very small income.”
https://en.wikipedia.org/wiki/Roi_fain%C3%A9ant