Larisnar version
Bone golems are crafted by the elves.
Sometimes the elves don't raise the dead - they just use them for spare parts.
Necropolis Sect version
A Sect War Golem made from all different kinds of bones, to ensure that the structure doesn't turn into a Skeletal, break loose of Necromantic control and kill everything in sight. By having a dozen spirits fighting for control, it is rare that any one spirit gets the upper hand. While the bone golem does not have much of a mind, it is able to understand simple commands from its masters and perform its bloody duties without question.
It takes the skills of a master necromancer to build and animate one of these morbid machines. Bone Golems are neither magespawned nor true undead, and have no real intelligence. They are "programmed" by their creators to accept simple orders, identify threats, and fight with reckless abandon. Still, Bone Golems are capable of assessing danger and calculating when to retreat and focus their dark energies on regeneration.