The creature Gothmog at the Siege of Minas Tirith

[Inziladun]

Originally Posted by Gordis

Here is the case when he is called Angmar:

So, why not Morgul?

It appears to me 'Angmar' simply refers to the region.

For at that time the realm of Angmar arose in the North beyond the Ettenmoors. ........ [The lord of that land was known as the Witch-king, but it was not known until later that he was indeed the chief of the Ring-wraiths, who came north with the purpose of destroying the Dúnedain in Arnor, seeing hope in their disunion, while Gondor was strong].

Appendix A ROTK

If he was 'the lord of that land', and himself called Angmar, why was he known as 'the Witch-king?