I assume you mean Khamûl who was said to have been a king of the Easterlings during the Second Age. It would probably be brief, but might be interesting. I think that we know more about him as a Nazgûl than as a man.
Note that Khamûl might not have been the only Easterling to become one of the Ringwraiths; he's just the only one that we know anything about. (EDIT: Apologies if that comes off as too pedantic.)
How much do we know about the other Ringwraiths? I do not believe I am wrong in saying that the Witch King was a Nazgul, was he?
The Witch-king of Angmar was the Lord of the Nazgûl and was almost certainly a Númenórean lord. His Ring was the most potent of the Nine. However, his real name is unknown.
I thought he was the Lord of the Nazgul, but I forget things easily, so I wasn't sure..