There is One God in middle earth. One God that created the Ainur.
Melkor rebelled like Satan. Sauron was once fair but was also corrupted, and is only a lieutenant of Morgorth/Melkor.
I don’t see dualism at all here. It is a monotheism, Eru who is also called Illuvatar is God.

I have studied Tolkien and his works for more than twenty years and have continued to discover the Catholicity of his work.

I have come across a few trad parents when I taught in an SSPX who were Puritanical when it came to literature. Why read the pagan classics? Why read certain Shakespeare plays and so on. Theirs was not a Catholic mindset but again Puritanism disguised in Trad Catholic wrappings.

Any who rail gainst Tolkien protest way too much.

Before the creation of Eä and Arda (The Universe and the World), Melkor was the most powerful of the Ainur, the "angelic beings" created by Eru Ilúvatar (analogous to God). Melkor, dissatisfied that Eru had abandoned the Void, had sought to emulate his creator and fill the Void with sentient beings. This, however, required the Flame Imperishable, the Secret Fire, which belonged to Eru alone; though Melkor searched for this, he could not find it. In what he hoped would be an alternative expression of his own originality and creativity, he contended with Eru in the Music of the Ainur, introducing what he perceived to be themes of his own.[T 8]
During the Great Music of the Ainur, Melkor attempted to alter the Music and introduced what he believed to be elements purely of his own design. As part of these efforts, he drew many weaker-willed Ainur to him, creating a counter to Eru's main theme. Ironically, these attempts did not truly subvert the Music, but only elaborated Eru's original intentions: the Music of Eru took on depth and beauty precisely because of the strife and sadness Melkor's disharmonies (and measures to rectify them) introduced. Unlike his fellow Ainu Aulë, Melkor was too proud to admit that his creations were simply discoveries made possible entirely by Eru. Instead, Melkor aspired to the level of Eru, the true creator of all possibilities.[T 8]
Since the Great Music of the Ainur stood as template for all of history and all of material creation in the Middle-earth cycle (it was first sung before Time, and then the universe was made in its image), the chaos introduced into the Music by Melkor's disharmonies was responsible for all evil in Arda, and everything in Middle-earth was tainted or "corrupted" by his influence.[T 8] Tolkien elaborates on this in Morgoth's Ring, drawing an analogy between the One Ring, into which Sauron committed much of his power, and all of Arda—"Morgoth's Ring"—which contains and is corrupted by the residue of Melkor's power until the Remaking of the World (analogous to the Apocalypse).[T 9]

Please, stop posting nonsensical ad hominem comments! Start commenting specifically on the work of Tolkien instead! Same for Kazimierz and his "Puritanical SSPX parents". Please, address what's being presented here in this thread, Mr. Judenviertel von Krakau.

All of the works of Tolkien are works of fiction, meaning they are not true, a fairy tale. I do not understand why all the angst and anger over fiction. I have read the Hobbit and the Trilogy twice and enjoyed them immensely, but I always knew that the were fiction, you know like an adult.

And heresy is an offense against Our Lord. Heresy is always fiction an never true or real.

Stanley N said it before on page one of this thread. Tolkien's fabulous creation is tainted or "corrupted" by Morgoth's/Melkor's disharmonies:

Again, to be clear, I like LOTR and the Hobbit. They're among the best English literature has to offer (certainly from the 20th century), with deep understanding of human nature, sin and virtue.

You cannot speak against the sacred cow of Tolkien.