From Discworld & Terry Pratchett Wiki
The Palace Guard constitute the main security force for the Patrician's Palace in Ankh-Morpork, as well as convenient muscle for the ruler of the city. Unlike the City Watch, who serve the Law first, the Guard are subject to the sitting ruler's commands above all. During the brief reign of the noble dragon King in Guards! Guards!, members of the Guard painted images of a dragon on their breastplates.
Skully Multoon is one of the few named Palace Guards.