The subject of this article originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
Where the other Nazgûl were slowly swallowed by the taint of their rings, not being fully dead, The Tainted is a wraith who gave himself wholly and willingly to Sauron. Now all natural things rebel in his presence, vegetation withers, animals sicken and bold warriors cower. It is an abomination whose merest presence is poison to life, honour and hope.