Names of The Nazguls

[Gorthol]

this is something i never got. would someone please tell me who Gothmog was! i thought he was a balrog under the service of Melkor, but then i read in an unofficial book he was a Nazgul!

The "Gothmog" referred to in the older writings concerned with the first age, are the Lord of the Balrogs, killed by Ecthelion in Gondolin. Also called "Morgoth's son". The later "Gothmog" in LoTR is the lieutenant of Minas Morgul, he was no Nazgûl but a black numenorean much like the "Mouth of Sauron", the lieutenant of the Dark Tower..