An obdurate is a human who is both incapable of learning Magery 0 and possesses Magic Resistance. Obdurates can only be human, although the reason for this is not known. Obdurates are highly sought out for their abilities and are frequently employed as bodyguards, or by the Mage Guild for handling potentially dangerous magical artifacts.
The word obdurate has been shamelessly stolen from L.E. Modesitt’s Imager Portfolio series.