More in the defunct course lecturette series: this from erstwhile DU class Hobbits and Heroes. This lecturette was during our discussion of Return of the King, so by that week we had read the whole trilogy plus The Hobbit, as well as various and sundry essays and things. ~Jenn
Corruption and Redemption
A Brief History of the Origin of Evil in Middle-Earth:
Melkor (“he who arises in might”) was jealous of Eru [the One] already before Arda [the world] was created, and wanted to be king of other wills himself. When Eru revealed the results of their song to the Ainur [Vala and Maia], Melkor was one of the first to descend into it, mainly from this desire.
…when the Valar finally rested, he and his followers (downfallen Ainur, like Sauron and the later Balrogs) attacked their dwellings and destroyed their Two Lamps (precursors to the Two Trees and the sun and the moon).
…the Noldor first named him Morgoth, “dark destroyer of the world”. With the aid of Ungoliant [mother of the giant spiders, including Shelob] he also managed to destroy the Two Trees and bring darkness to Valinor, before he fled.
Because Morgoth dispersed his essence all over Arda, it is said that all of Arda outside of the Blessed Realm has some evil in it, this being the Morgoth-element.
The essence of evil in Middle-earth centers around selfishness, the desire to be “king of other wills,” the intense protection of ego to subordination of all else, and the “lack of imaginative sympathy” which is usually the fatal flaw by which evil is vanquished. We have to remember that Sauron is not the biggest baddie of Middle-earth: Morgoth (still in chains and diminished in the times LOTR takes place) really is the Root of all Evil, having had Sauron, the Balrogs, and Ungoliant as his best subordinate servants back in the day. Even though Sauron is an extremely powerful, if non-corporeal, presence in LOTR, we must remember that he is but a Maia (like Gandalf and Saruman), whereas Morgoth is a Vala, a higher being and much more powerful. Thank goodness Morgoth is out of commission in Middle-earth at the time of our story—if Sauron, his lieutenant, can wreak this much damage and fear, imagine what Morgoth himself must have done back when he ruled from Utumno.
“Nothing is evil in the beginning. Even Sauron was not so.”
Well, Gandalf should know, he being of the same race as Sauron, and most likely knew Sauron before Morgoth convinced him to turn to evil. The worst kind of evil, the kind which flatters and seduces, is examined over and over again in LOTR; each time a baddie is defeated, he is given a chance for redemption, and true colors will out when one looks at the choices each character makes. Sauron is a terrifying Eye, a void with a dominating presence (oxymoron? maybe), but back before he died and came back (like Gandalf) he was handsome and well-spoken, enough so to fool the Elves into forging Rings for him. His deception is much akin to Saruman’s voice: betrayal masked behind a fair facade.
Boromir’s Fall / Smeagol’s Fall
Both these characters are irrevocably seduced by the domination of the Ring: both fall into the trap of wanting to possess it (Smeagol actually does possess it, to his ruin), and both are ultimately redeemed in death.
When Boromir tries to seize the Ring from Frodo, he subsequently falls on his face, then weeps, realizing what he has done. He understands, finally and too late, why Elrond and the wise ones in charge did not want to use the Ring, but destroy it. He dies defending the hobbits Merry and Pippin, and confesses his sin to Aragorn before he dies, thus redeeming his honor.
Smeagol and the Ring are inseparable: he is addicted to it without hope of healing–the Ring cannot be destroyed while Smeagol is alive. When Frodo, at the Crack of Doom, gives in to the Ring’s power and claims it for his own, only Smeagol’s self-sacrifice (in the guise of mad desire for the Ring) makes it possible for it to finally be destroyed. Smeagol’s long life of sniveling addiction is redeemed in that last act, and though he does not consciously realize it as such, it is self-sacrifice. He is the Ring, and for it to be destroyed means he too must be destroyed.
Saruman’s Fall / Denethor’s Fall
Saruman and Denethor are more men of intelligence than men of action, like the above fallen figures. They both, in their peak of good work, prize knowledge greatly, and in particular the knowledge of the darker arts. Both have one of the palantir and both use it, but, foolishly (as in the seductive trap of the Ring) they both think they can wrest its power from Sauron and rule as a great power in his stead. This is how both these wise characters come to their doom: they begin to think like Sauron: of domination, and so play right into his hands.
Saruman does not take the chance for redemption given him, not when Orthanc is first taken, nor later when he meets the leftover party on the road as a beggar. His corruption is not easily erased, however, as the hobbits find out when they return to the Shire. He has ruined the Shire on his way down, and even in death there is no redemption for him.
Denethor, being a proud man of the blood of Numenor, is easily tricked into believing he has control of his palantir, because Sauron is quite familiar with such pride, and can easily feed him the information he chooses until Denethor collapses into despair and suicide (and filicide. Is that a word? It is now). The path Denethor follows is no doubt just like the fall of the Nine Kings of Men who are now the Ringwraiths: if Denethor had had the One Ring (or any of the Rings of Power), he’d become a Ringwraith as well. As it is, his life is over even before Gandalf and Pippin arrive. He achieves no redemption in his death, as suicide is not an honorable way to go in Middle-earth. Here, Gandalf admonishes Denethor, already in madness, against the sin of suicide (emphasis my own):
“Authority is not given to you, Steward of Gondor, to order the hour of your death…and only the heathen kings, under the dominion of the Dark Power, did thus, slaying themselves in pride and despair, murdering their kin to ease their own death.”
Pride and despair: the center of the self-fear that is evil manifest in Middle-earth. How does one defeat such evil? With humility, of course: humility, empathy, and hope.
 Go to the “Middle-Earth” wikipedia link, and enter “Morgoth” to read the detailed summary. Bracketed explanations and italicized emphasis are my own.
 From “Sauron and the Nature of Evil,” Master of Middle-Earth, Paul H. Kocher