The skeleton is the bones of the dead raised by magic into a sword-bearing form, and it is one of the first monsters included when tabletop role-playing was first published in 1974. Having no flesh, it resists cutting, and lacking a self, it moves only on command.
The image of a soldier of bare bones is drawn straight from medieval folk iconography such as the danse macabre, belonging to shared imagery rather than any one work’s trademark.