Who were the nine human kings who wound up as the Nazgul? Were they Numenorians? Easterlings?
Khamul was given as the name of one of the wraiths in Unfinished Tales, but the others seem not to have names. The writers at Iron Crown made up names for the other eight for the MERP game they wrote.
I assume they were kings of different kingdoms, all ensared by the rings pretty much concurrently. I’d hate to think that they were nine successive kings of the same realm… You’d think that after six or seven turn into wraiths, the next one would look at his shiny new ring and go “hey, WAIT a minute!”
IIRC, some were indeed Numenoreans. I’ll have to check my resources to find out just how much was said about them.
Tolkien only gives background for two, the de facto leader and second in command. All nine were “kings who were ensnared by the rings” – but of what, where, and when is not specified.
The Witch-King (Nazgul #1) was King of Angmar, the realm north of Arnor (it shows on the map in Unfinished Tales).
Khamul (Nazgul #2) was “the Black Easterling” and hence was a king in Rhun, unless Rhun is or was a unified realm in which case he would be King of Rhun. (Tolkien doesn’t make this clear – but the Easterlings are from Rhun.)
I dunno, but the seventh one had a really great rack.
Polycarp, I was under the impression that he ruled Angmar as a ringwraith. I believe he united the men in that area under his rule, to oppose the power of Arnor. His ringwraith status pre-dated the founding of Arnor.
Also Rhun was just one kingdom of the East. There were many, many others.
I’ll check my sources at home.
Cross-continuity humor gets me every time… chuckle…
You right!! 
As I thought, the Witch-King came to Angmar in 1300 TA, to sow strife among the Dunedain of Arnor. He’d been a Nazgul for centuries by that time.
http://www.annalsofarda.dk/annals-of-arda/Others-index-tables/Others/Murezor.htm