Potestaat was the title of a supposed governor of medieval Friesland. According to the legendary Karelsprivilege, a 14th-century forgery, Charlemagne had first granted the title of potestaat to Magnus Forteman. He and most of his early successors were entirely fictional, invented later by pseudohistorians in order to argue in favour of the notion of Frisian freedom. The title potestaat does not appear in historical documents until 1470. It became popular after 1578, when the idea of the inherited office of potentate was linked to the new office of stadtholder, which was held by the House of Nassau-Dietz.
In 1851, Wopke Eekhoff compiled the following list in Beknopte Geschiedenis van Friesland ('A Brief History of Friesland').