Characters who can easily defeat Sauron are; his Creator Eru Ilúvatar, his old master Melkor, and the Valar. Others who could overcome him would be Ungoliant who physically dwarfed Morgoth, and some great Maiar of Valinor described as almost as great in power as the Valar themselves.
When he couldn't accomplish that, he began to war against the other Valar and rule over Middle-earth with his fires and evil creations. With this turn to darkness, Melkor became known as Morgoth. While at war, Morgoth lured many beings to his cause.
Morgoth, the first to reign terror upon Middle-earth, was more powerful than Sauron and commanded an army of dragons and Balrogs. While both Morgoth and Sauron were cunning, Morgoth's rule and terror lasted longer and his corruption spread further, making him more formidable in the Lord of the Rings universe.
Ultimately, the only being more powerful than Morgoth in his prime was Eru Ilúvatar. Only the combined effort of the Valar could stop Morgoth, and only after countless battles. Sauron might have bested his mentor under certain circumstances, but Morgoth is the greater Dark Lord by every metric.
Finally Sauron came out to fight Elendil and Gil-galad face to face. When Elendil fell, his sword Narsil broke beneath him. Isildur took up the hilt-shard of Narsil and cut the One Ring from Sauron's hand, vanquishing Sauron.
Why Was Sauron so Powerful? (Even Among Maiar) - Middle-earth Explained
Who is Sauron most afraid of?
Sauron's deepest fear was that Aragorn would use the Ring against him. With its powers of domination, Aragorn could comfortably take over the entirety of Sauron's dark army. Though this would eventually corrupt Aragorn, it would allow him to destroy Sauron and take his place.
Additionally, while he was in his weakened state, Galadriel could hold him off through the power of will alone. However, if Sauron had his One Ring and faced off in a battle against Galadriel, it's unlikely that there would be much she could do.
"So I think in his pitch to Galadriel, it cannot mean that he loves her or that there's any kind of romantic relationship. There should be no ambiguity around the fact that Sauron is evil — he's terrible, and he's using Galadriel to enhance his power."
There's no question that Sauron is among the strongest beings in Middle-earth, so powerful that even when defeated, he lay dormant and gathered strength in non-corporeal form. Sauron poured his power and will into the One Ring so that as long as it existed, he could never be truly defeated.
Meanwhile, a few faithful Númenóreans, led by Elendil, were saved from the flood, and they founded Gondor and Arnor in Middle-earth. Sauron still considered them his hated enemies and he launched a pre-emptive attack on Gondor in S.A. 3429.
If it was taken to Denethor by Faramir, again game over. Generally speaking anyone either claiming the Ring or “keeping it safe” would have all but ensured Sauron's victory. With one exception. According to Tolkien, the only one who would pose a danger to Sauron if he claimed the One would be Gandalf.
Gandalf the White is particularly good as a counter to Sauron because he can bring troops - and as was mentioned above, he doesn't need to bring yet-another-expensive-hero to the party (like Galadriel usually does).
Though wizards are technically Maiar, they do not possess all the same abilities in their wizard forms. This is why, despite Balrogs and Sauron also being Maiar, Gandalf wasn't evenly matched in his wizarding form—especially as Gandalf the Grey.
This Gandalf defeated Saruman, so he is also above Saruman. However, he is still les powerful then Sauron. But, there are other beings in Middle-Earth at that time (Third Age). For example, Galadriel and Elrond.
Because Sauron lost his Ring, his power severely diminished, and it took him thousands of years to rebuild his power. Even after Sauron declared himself again, his sole focus was on finding the Ring, not on solidifying his dominion.
In his notes, Tolkien remarks that Sauron saw Galadriel as his equal. Add that to the fact that she's untrusting of Sauron (yes, even when he's in his Annatar guise) and an unwavering, single-minded force, and it's more likely than not that Sauron feared Galadriel — or the potential she held to upend his plans.
After trying and failing to murder Sauron to save Middle Earth in the final episode, Season 2 of The Rings of Power could see Galadriel blinded by rage at Sauron's betrayal and deception. One thing is now certain; the friends, and even potential lovers, have become sworn enemies.
This was how Halbrand/Sauron actor Charlie Vickers played the part, saying he believed the proposition to become his queen came "from a place of selfishness." Regardless, Galadriel denied the proposal. However, her answer did not come without hesitancy -- which was exactly why Celeborn needed to be out of the picture.
Thus, Galadriel's dark form in Jackson's The Lord of the Rings personified what would have occurred had the Lady of Lothlorien given in to temptation and taken the One Ring for herself. She would have succumbed to evil because the Ring was indomitable, even with her power.
Though neither is someone you'd wish to annoy, Galadriel is generally considered more powerful than Elrond in Lord of the Rings. Not only is she older than her Rivendell counterpart, but Galadriel witnessed the light from Valinor's Two Trees, giving her a mystic quality.
Melkor is the most powerful of the Valar but he turns to darkness and is renamed Morgoth, the primary antagonist of Arda. All evil in the world of Middle-earth ultimately stems from him. One of the Maiar of Aulë betrays his kind and becomes Morgoth's principal lieutenant and successor, Sauron.
It was said that Morgoth hated and feared the House of Fingolfin most among the Houses of the sons of Finwë, especially Fingolfin's son Turgon, as it was prophesied that his doom would come from the House of Turgon.
While Morgoth doesn't appear in The Lord of the Rings or The Hobbit, he plays a significant role in The Silmarillion and Tolkien's other writings, and his reign of terror had a far bigger impact on Middle-earth history than Sauron's — as seen in Amazon's The Rings of Power series.
