Of Pharazon and Miriel

[Urwen]

Speaking of which, I heard your theory that Witch-King is Tar-Telperien. Now hear out mine regarding who it is.

Witch-King used to be of Race of Men.

"They were once Men. Great Kings of Men. Then Sauron the Deceiver gave them Nine Rings of Power." - Aragorn

Now, which other ruler was Sauron closest to? Pharazon, naturally. But would Sauron really think of Pharazon as someone worthy enough to be his top lieutenant and the leader of his main strike force? I don't think he would. Was there someone else around that he would think was worthy enough? As it happens, there was.

So he convinced Pharazon to embark on suicide mission, along with majority of his men. Then he gave one of Nine Rings of Power to Zimraphel, convincing her that she'd be able to undo Pharazon's work and all the corruption that happened in Numenor, and that she'd be able to bring Elves back. It was this that convinced her to take it. With the help of the Ring, she survived the Downfall.

The Ring slowly corrupted her and eventually turned her into one of the Ringwraiths. Because of her noble blood, Sauron made her a leader of the Nazgul.