Gothmog and the Mouth

[Boromir88]

It's not clear that The Mouth was a Black Numenorean, that is only what was said about him, but he was clearly high up in Sauron's hierarchy, and had forgotten his true name (just as the Nazgul remain nameless).

Although I don't think he was one of the blue wizards (as interesting of a question as it is that got me thinking what if?), because in the very late writings Tolkien told a bit more about the Blue Wizards. After Saruman had went East with them and returned alone CT mentions that the two blue wizards were Maia of Orome and can be assumed their mission was to travel (and stay) to the unknown lands of Middle-earth (reasons for why they stayed in the East). There they played a significant role in resisting Sauron and limitting the numbers who joined his armies. However, I think this essay on the Ithryn Luin was very late (I want to say 1970 or '71?) and not sure if it can be considered canon. I'll see if I can dig it up.