[Boromir88]

With Gothmog, nothing is known for sure, anyone's guess is as good as the next. Afterall he only gets this one sentence in The Lord of the Rings:

He now was destroyed; but Gothmog the lieutenant of Morgul had flung them into the fray; Easterlings with axes, and Variags of Khand, Southrons in scarlet, and out of Far Harad black men like half-trolls with white eyes and red tongues.~The Battle of Pelennor Fields

I've always felt this ruled out the 'orc' possibility. Because if you notice Gothmog is commanding a group entirely composed of Men. Sauron (nor Saruman for that matter) seem like people who would put Orcs in high positions when it comes to their hierarchy. Saruman didn't trust Orcs as gatekeepers...so he used Men. And the highest/most trusted servants of Sauron's were the Nazgul (once Men) and the Mouth of Sauron. Therefor, Gothmog most likely seems he would be a man (or once a man - a Nazgul).

The reason I don't think Gothmog was a Nazgul, I think TM has put it the best way. The Nazgul's lack of identity is a symbolic matter. Tolkien plays with this idea of the importance of 'names.' If you have a name, you have an identity, you have this sense of self and free will. If you have no name (or forget your name entirely) than there is no identity, you are completely controlled/have no free will. Prime example being the Nazgul, being slaves to Sauron...they lost names and their identity. Let's take Gollum...his name was Smeagol, however people soon labelled him Gollum because of the noises he made. He loses touch with Smeagol and becomes Gollum (as he becomes controlled by the Ring).

As far as Tolkien calling one of his Nazgul 'Khamul.' There are a thing to consider. 'Khamul' was only mentioned in Unfinished Tales, no where else (and probably the important one - The Lord of the Rings) does the name 'Khamul' for one of the Nazgul show up.

One quick comment here for Ninja:

Well, if he was a Nazgul, then there would have had to be an ancient king named Gothmog

The whole thing of the Nazgul being 'Kings of Men' was entirely made by the movies. In The Silmarillion we are told that 3 were 'Numenorean Lords' and that after they received their rings they became 'great kings, warriors, and sorcerers.' As far as the 9 Nazgul being 9 Kings of Men, that was something from the movies.