The Talons are the elite personal guard of the Black Hand of Sauron. The Black Hand was schooled in sorcerous arts at the side of the Necromancer, and he personally draws forth the Talons from their spawning vats at Barad-dûr. They are tested in battle immediately after they are dragged, screaming, into a world of anger, hatred, and fury.
There are always five Talons and whenever one falls in battle his body is returned to the vats where his death can feed the creation of his successor. If his corpse can not be successfully carried back to Barad-dûr, then the remaining Talons are sacrificed in his stead.