|This article is about an older version of DF.|
The Royal Guard is activated by the arrival of any civ leader noble. For most forts this will be the Baron, but could be the Count, Duke or King if you jump a couple of steps up the social ladder at once. Dwarves are assigned to the Royal Guard in the same manner as the Fortress Guard (from the iew -> references menu), and act in most respects like the Fortress Guards do. They are mainly involved in the collection of taxes, but they will also spar in the barracks and can be assigned weapons and armor.
Nobles such as the Baron and consorts will receive unhappy thoughts if there are not enough Royal Guards. You need 1/20 of your population, rounded down, in the Royal Guard to avoid this.