The new Lord of the Rings series will cover the Second Age era of Tolkien’s saga. Much like the six movies of Lord of the Rings and The Hobbit, the series will almost surely feature Sauron as the main villain. But the creator of the Ring wasn't always evil.
Going only by Peter Jackson’s original trilogy, Sauron is a rather elusive and simple character. When he is introduced at the beginning, he is called “The Dark Lord, Sauron” who “poured into this ring all his cruelty, his malice, and his will to dominate all life.” It is therefore implied that Sauron was evil from the beginning; however, that is not the case.
The fallacy stems from the fact that the trilogy never goes in-depth into Sauron’s backstory. Most of his “appearances” (if you can call them that) after the initial explanation of the ring’s backstory are as the all-seeing eye atop Mordor’s tower: a disembodied, intimidating god-like presence. Rather than an actual character, Sauron appears to be an idea, a form of evil personified.
But there is a backstory to the actual character that's seen in the beginning of The Fellowship of the Ring and is further fleshed out in J.R.R. Tolkien's book, The Silmarillion. Sauron was a Maiar, a spirit originating near the beginning of time. Those Maiar descended upon Arda, the world of which Middle-earth is a part of. Other Maiar include Curumo and Olórin, better known in Middle-earth as Saruman and Gandalf.
Like Saruman, Sauron was a student of Aulë the Smith, essentially one of the original beings created by Eru, the deity of Arda. His original name was Mairon, which translates into “The Admirable.”
Mairon was especially known for his love for order, a trait that essentially turned him into a perfectionist. While his task was to organize Arda for the creatures who were to inhabit it, his obsession with order was eventually his downfall. This lead to a fascination with the first Dark Lord, Morgoth.
Morgoth himself was the most powerful Ainur (the race that consisted of Maiars and Valars) and had turned to the dark side. Morgoth’s goal was to control or destroy Middle-earth. It was also during his service to Morgoth that Mairon received his new moniker of Sauron (which means “the abhorred” or “the abominable”).
After Morgoth was defeated, Sauron hid in Middle-earth, only to reappear after hundreds of years in Mordor. Unlike the First Lord, Sauron’s goal was never to destroy Middle-earth. Instead, he wanted to rule in total power, giving him complete control over maintaining order as he saw fit.
Sauron was not always evil; he is rooted in good. It is the excess, the obsession with his organization, that turns him into the Dark Lord. In fact, it could even be argued that, while he is the main antagonist in the Lord of the Rings trilogy and undoubtedly carries evil intentions, he is not evil personified even then. His motives, while egoistic and immoral, stem from a personal obsession with orderliness – something immaterial and morally neutral. His obsession, though, leads to unequivocally evil actions.