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.
Sauron's evil grew from his original servitude to Morgoth, the world's first Dark Lord, into his own obsession for "mastering" all things in Middle-earth through wicked means. After Morgoth's fall, Sauron was fully autonomous and committed, for two Ages, to gaining tyrannical control over Middle-earth.
The corrupting effect of power in the book is not limited to the Ring. Sauron was already corrupted when he chose to put much of his power into the Ring to gain further control of Middle-earth.
The wizard called himself "Saruman of Many Colors" and "Saruman Ring-maker," indicating his covetous nature led him to try to make a Ring of Power for himself. Still, it lacked the strength of Sauron's or Gandalf's, so the former White wizard joined the Dark Lord in an attempt to claim some of his power.
Originally known as Melkor, Morgoth is essentially the Lucifer of Tolkien's story. Like the devil, Morgoth was one of the first children created by the God of Tolkien's world, but succumbed to jealousy and greed, especially over the creation of other races, and was duly disowned by his fellow Valar.
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.
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.
The outcome is that Galadriel is able to penetrate Sauron's mind and issues a single command "Go back to the void from whence you came!" Unable to resist her any longer, Sauron screams and flees with the Nine.
Bloodlines are very important in Tolkien's stories, and it makes a lot of sense that Sauron would fear the great-grandson of the man who cut off his hand. Aragorn carried the blood of Numenor with him. His genetic connection to the heroes of the Second Age established him as a dangerous opponent of Sauron.
The majority of her powers come from her Ring of Power, Nenya, the Ring of Water. The ring, also known by the names the White Ring and the Ring of Adamant, is one of the three Rings of Power given to the Elves of Middle-earth in the Second Age.
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.
Despite her power, Galadriel couldn't match Sauron's ability to wield the One Ring, and it would have ultimately turned against her. Even if she managed to carry the ring, Galadriel's ambition and power-seeking nature would have eventually led to her corruption, making her unfit to deal with Sauron's weapon.
According to J. R. R. Tolkien, yes, Sauron was afraid of Smeagol, that is, Gollum. He was not afraid to torture him for information, nor to keep him in prison for a while. But, after Sauron had gotten all that he could out of Gollum, the sensible thing to do was to kill him.
"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."
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.
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.
Of course, once the Gray Wizard arrived in Isengard to ask Saruman about the One Ring, he discovered that his "old friend" had turned from the ways of good, instead deciding to serve Sauron in an attempt to claim power (and even the One Ring) for himself.
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.
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.
In the final minutes, Sauron confesses that he's been manipulating Galadriel since they first met — using her as a way to get back to Middle-earth to fight back against his enemies in the Southlands and indirectly form the land of Mordor but also to get closer to Celebrimbor and the Elven smiths.
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.
Eventually, Morgoth was bound in chains by the Valar and thrown into the Void, leaving the permanent damage his evils had done, and his former lieutenant Sauron, to trouble the world. One day, according to a prophecy, Morgoth will rise again in great wrath, but he will be destroyed in the Dagor Dagorath.
Mainly Eru for going against his will and siding with Morgoth. After the fall of Morgoth and Sauron's rise to power his primary nemesis would be a collection of leaders who opposed him: Gil-Galad, Elrond, Cirdan, Galadriel, Celeborn, the line of Elros and the Numenoreans.
