Dush-Hai

Long ago, the Orcs of Mount Gundabad brought clerics and mages from Mordor to match those of the Men and Elves they fought.Sauron created goblins capable of wielding the Essence (by selective breeding) before he had sufficient Men and dark Elves to serve him, and still preserves the line. The Lord of the Nazgûl soon found it easier to train evil Men to his service, as they weregenerally more magically adept than the brightest of Orcs. However, the breeding continued in a desultory fashion, to meet the Orc tribes' needs for magic, and a whole generation of these Orcish mages and shamans were pressed into the Witch-king's forces.