While Sauron is indeed one of the evilest entities in Middle-earth history, he wasn't always so, as The Rings of Power's premise states that "nothing is evil in the beginning." In fact, there were moments in the Second Age, after the fall of Morgoth, and even during the War of the Ring (depicted in The Lord of the ...
Sauron was originally Mairon, a Maia of Aulë the Smith, created before history. In the Second Age, he invented the One Ring to help him attain dominance of Middle-earth.
While the book version of Sauron is Pure Evil, due to being a manipulative sadist, which was shown in The Silmarillion, his lack of personality and motives in both the Ralph Bakshi and Rankin-Bass movies renders him not even close to qualifying in those versions.
For a brief time, Sauron repented of his evils and even sought to heal Middle-earth. Yet, that didn't last long. In trying to heal and order Middle-earth, his pride got the best of him. He was the only one who could properly order the world.
Purpose. The One Ring was forged by the Dark Lord Sauron during the Second Age to gain dominion over the free peoples of Middle-earth. In disguise as Annatar, or "Lord of Gifts", he aided the Elven smiths of Eregion and their leader Celebrimbor in the making of the Rings of Power.
Why was Sauron Evil? - Sauron's Philosophy | Lord of the Rings Lore | Middle-Earth
Why did Sauron become evil?
Wholly evil will
He explained that, like "all tyrants", Sauron had started out with good intentions but was corrupted by power, and that he "went further than human tyrants in pride and the lust for domination", being in origin an immortal (angelic) spirit.
In that brief moment, Sauron regretted ever forging the One Ring, for he now understood the possibility of him losing again was real. He had grossly miscalculated his steps, as, in his mind, Aragorn (Viggo Mortensen) was supposedly the person who bore the One Ring.
"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."
Sauron seemed to genuinely feel a connection to her, and part of that came from sensing the darkness inside of Galadriel. In that regard, his offer was really a seduction to the dark side.
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.
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.
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.
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.
Isildur used a broken sword to cut the Ruling Ring off Sauron's hand. Sauron was fatally wounded by Gil-galad and Elendil as Sauron killed them. Gandalf took the job of blocking the Balrog - and he was barely able to defeat the Balrog (in fact, he died in the process).
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.
Assuming the One Ring was destroyed, Galadriel's ring would also start to fade, causing Lothlórien to lose its glory and magic. So, when Galadriel refused the One Ring, she wasn't just sacrificing her desire to rule. She knew that she was sacrificing her kingdom and its well-being for the sake of peace in Middle-earth.
Sauron's only interest was an order or to work upon the world in an orderly state, even in the beginning, Mairon really had no love interest. Despite his deceptive attributes, he was a trickster and a seducer, he had little care for attempting to love someone.
For those that haven't read Tolkien's work, it's easy to see why many audiences suspect Gandalf and Galadriel are in love. After all, many of their interactions in The Hobbit trilogy practically scream romance. However, their relationship remains purely platonic in Tolkien's source material.
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.
Plus, he makes the compelling argument that while he lusts for power, she has a good heart and would help him remain good rather than turning to evil. But when it becomes clear to Galadriel that Halbrand/Sauron cannot tell the difference between “saving” and “ruling” Middle-earth, she rejects his proposal.
Sauron was the most powerful of the Maiar—primordial spirits created to help the Valar first shape the World. His original name was Mairon, which means "the Admirable," and as an immortal spirit born before the world's creation, he was able to perceive the Creator Eru Ilúvatar directly.
Sauron was severely weakened at that point in time, and they still barely defeated him. So, a fully-powered Sauron with the One Ring to boot would likely have been too much for them.
With the destruction of the ring, since it had so much of his native power, he would no longer have the power to build a bodily form after the ring's destruction. But he would still exist as an immaterial spirit since he was immortal in that form.
