In the beliefs of the Variags and the men of Khand, the Khûdriag-Ata was a holy or demi-god like man, chosen by the Tumrakhi and gifted with immortality.
In fact, Khûdriag-Ata was a role or masquerade invented by Sauron to deceive his mannish followers. The part was usually played by The ninth of the Nazgûl.