Dear HonoredRohan: I think that some of us are feeling over-Khamûlized by now (at least I do), so have some patience even as a newcomer here.
The slim information of that particular
Nazgûl (a man from the East, as well as his name) comes from the Unfinished
Tales, in which he is also confirmed to be "second to the Chief", with no other details given than a side note that he would have been black and particularly adept to perceive the presence of
the Ring, but also
the one whose power was most confused and diminished by daylight.
You can read more in Chapter 4 of the UT but expect to discover no more about his origin. Nonetheless, UT is really a delight to read; I recommend it very much.