Servitors were special probes that were in service to the Spear of Adun. When the Daelaam forces reactivated the arkship, it brought the servitors online. The servitors began severing the nerve cords from the protoss warriors in stasis.
Karax utilized many servitors in his service. They could place a temporary photon cannon and reclaim corrupted robotic units.
The purifiers created a variant of servitor.