keletons are probably the most common type of undead. They are easy to create, and the materials are easy to find. Bones from which the skeletons are made do not have to come from the same body. For this reason, a single walking skeleton can have several sources. Material from not only different bodies, but also different races can unite in it.
Skeletons are devoid of intellect, and so always precisely carry out orders of their master. They know no fatigue or fear, while their "sense of life" allows them to always find their target.
Because skeletons are the most common type of undead, not much equipment is required. Since several graves can be used to make one warrior, there is no shortage of weapons. Skeletons are predominantly armed with the weapons with which the bodies have been buried - often old rusty swords. A blow with such a weapon may not be strong enough to pierce good armour, but there is nothing worse for unprotected flesh than a bland rusty blade.
The Skeleton's bones are fragile and break even from fist blows, but are hard to hit with a pike or arrow, so skeletons are very good when fighting against archers.