[Legate of Amon Lanc]

Originally Posted by Kuruharan

This sort of throws my original thought into a bit of question because the Balrog was also a being with which Gandalf would have been familiar during the Music. It had changed to the point that Gandalf could no longer recognize it. How much more so with Sauron...?

Gandalf definitely forgot a lot when he was incarnated:

Originally Posted by UT; Istari

For it is said indeed that being embodied the Istari had needs to learn much anew by slow experience, and though they knew whence they came the memory of the Blessed Realm was to them a vision from afar off, for which (so long as they remained true to their mission) they yearned exceedingly.

I don't believe he at the moment remembered some Balrog or even Sauron who was singing with him in the Music. Also, he met them only before the descent to Arda (well, Sauron maybe even later, but still a long time ago), where they still did not have bodies and everything, so his perception of them was different.

Originally Posted by Ibrîniðilpathânezel

It seems to me that it's the other way around, that Gandalf was changed by the constraints of his mission in Middle-earth. He and the other Istari were sent in real bodies rather than a self-incarnate fana, partly for the purpose of diminishing their native abilities so there would be less temptation to try to rule the Eruhini by revealing their full power. Sauron and the Balrog don't have these constraints.

Yup, I also think so. But as shown above, I think it worked even the other way around.

I tend to wonder if he ever did figure out who Gandalf was, since the Mouth of Sauron appears to consider him more of a nuisance than a threat (although Sauron might've gotten confirmation via Saruman, and simply doesn't consider Olorin a threat, anyway, and wouldn't've told an underling even if he did).

I believe Sauron knew what Gandalf is, just did not bother to tell his servants, as many of them would not understand anyway. Although...

Originally Posted by UT; Istari

and none save maybe Elrond, Círdan and Galadriel discovered of what kind they were or whence they came.

So if we take this indeed literally, word-to-word, then Sauron did not know. Only Elrond, Círdan and Galadriel; and no one else.

Originally Posted by Kuruharan

There is some merit in what you are saying, but Sauron and the Balrog had undergone *profound* changes since the time that they had sung the Music.

I think it would be similar to the way that Manwe failed to recognize Melkor when the Valar defeated him in the War of the Powers.

Exactly (to the first). Yes, something like that (to the second).