Balrog and The One Ring

[Zigûr]

The most relevant passage about Sauron's attitude to Morgoth after the First Age is to be found in Morgoth's Ring:

Sauron was not a 'sincere' atheist, but he preached atheism,
because it weakened resistance to himself (and he had ceased
to fear God's action in Arda). As was seen in the case of
Ar-Pharazon. But there was seen the effect of Melkor upon
Sauron: he spoke of Melkor in Melkor's own terms: as a god, or
even as God. This may have been the residue of a state which
was in a sense a shadow of good: the ability once in Sauron at
least to admire or admit the superiority of a being other than
himself. Melkor, and still more Sauron himself afterwards, both
profited by this darkened shadow of good and the services of
'worshippers'. But it may be doubted whether even such a
shadow of good was still sincerely operative in Sauron by that
time. His cunning motive is probably best expressed thus. To
wean one of the God-fearing from their allegiance it is best to
propound another unseen object of allegiance and another hope
of benefits; propound to him a Lord who will sanction what he
desires and not forbid it. Sauron, apparently a defeated rival for
world-power, now a mere hostage, can hardly propound him-
self; but as the former servant and disciple of Melkor, the
worship of Melkor will raise him from hostage to high priest.

This has always suggested to me that Sauron advocated Melkor-worship in Númenor out of opportunism and pragmatism, not genuine belief. As a hostage and prisoner in Númenor it would have been very unlikely that he could have put forward himself as their new religious figure and be successful, but he can put forward someone else, one about whom the Eldar had perhaps rarely spoken, and perhaps therefore appeared to be "forbidden" (and thus appealing) in the lore of Númenor which, by then, had been estranged from the Eldar and Valar for some time.

As for other places, it seems as if Sauron tended to be worshipped as a god himself. Professor Tolkien observes in Letter 131 that Sauron's empire, even in the Second Age (before he went to Númenor in fact), was an "evil theocracy (for Sauron is also the god of his slaves)". He also appears, according to The Lord of the Rings, to have been worshipped by the Black Númenóreans in some parts and/or at some, possibly later, times: "they established their dwellings in Middle-earth during the years of Sauron's domination, and they worshipped him, being enamoured of evil knowledge."

We also know, however, that "By the end of the Third Age (though actually much weaker than before) he claimed to be Morgoth returned." (Letter 183) This suggests to me the possibility that Sauron exploited Men's uncertainty about who or what their dark god actually was in order to conflate himself with that person; it seems possible to me that some Men at least did not know that there was any difference between Morgoth and Sauron. Sauron, however, "demanded divine honour from all rational creatures", which suggests to me that he ultimately wished for himself, not Morgoth, to be worshipped as a god, and that he only used Morgoth's legacy when it enabled his own power to do so. According to Morgoth's Ring, he may actually have seen Morgoth as a failure after the First Age, not an object of worthy veneration:
"He probably deluded himself with the notion that the Valar (including Melkor) having failed, Eru had simply abandoned Eä, or at any rate Arda, and would not concern himself with it any more."

I should point out, however, that this is something of a later character development. In the original Númenor story composed in the early 1930s, at the time of The Lost Road and before any other aspects of the history of the Second Age were invented (and before the Third Age was invented at all), Sauron did not have this personal agenda; he's actually more like a puppet of Morgoth's will, or at least receiving instructions from Morgoth from afar. In this period Sauron appears to have been conceived of more as Morgoth's representative; in the later developments of the narrative Morgoth no longer seems to have much capacity, if any, to instruct or communicate with his former servants from the Void, and Sauron takes on the role of a replacement with his own, separate ambitions.

As for the Balrog, I don't recall any material in The Treason of Isengard or elsewhere which speculates too heavily on the nature of the Balrog, although I think there is speculation, abandoned in later re-drafting, that it might have served Sauron. I'll have to check later. Just wanted to get the "How sincerely did Sauron worship Morgoth?" discussion out while it was fresh in my mind.