Nazgûl

Also known as Nazgul, the Ringwraiths are what you get when you give nine perfectly ordinary mortal kings each a ring of overpowering evil. Tend to dress in black robes, screech a lot, and be extremely hard to kill, what with being dead already. Taking on a Ringwraith is a Very Bad Idea.

In Suefic, Sues are sometimes Daughters of Ringwraiths, notably the Witch-King of Angmar. It's also not unknown for badficcers to create an Extra Ringwraith.