It boots nothing to avoid his snares, for they are ever beset with other snares, and
life and death are too intimately intergrown to be severed from each other.
The Wounded Land, Stephen Donaldson
Lord Foul the despiser is the Bad Guy in the Chronicles of Thomas Covenant. But he isn't just your bog standard fantasy novel evil guy who everyone must get together to defeat. Although he has the trademark destroy the world aims in life, his method of operation is slightly more complex. His success will be complete when you become that which you hate and give in to despair.
To fully understand this write up, you must know that in the book Thomas Covenant suddenly finds himself in a place called The Land. He is called the Unbeliever because he insists that the land has no reality and is a dream which exists solely in his head.
Myth of creation
When the Creator made the world, he was unaware that the son or brother of his thought, Lord Foul, had set out to spoil it. Angered by this, the Creator cast down Lord Foul and imprisoned him in the Arch of Time (this means that Lord Foul is stuck in this particular world). The Creator is left with a dilemma. He dares not free Lord Foul; but he is responsible for this particular world and wants to help its people fight against Lord Foul. This he cannot do without reaching into the world and thereby breaking the Arch of Time.
So Lord Foul is not a redeemable character. He is thoroughly bad and his sole goals are destroying and enslaving the Land and breaking the Arch of Time. This is where Thomas Covenant comes in. He was summoned to the land because his white gold ring is the only tool which could free Lord Foul. It is also the only way by which Lord Foul could be defeated without the Creator having to release him. The philosophical crux lies in the fact that tools are only as powerful as those who wield them. If either Lord Foul or the Creator coerce Thomas Covenant into doing something, he becomes their tool; and since they are both powerless in this situation, they must both hope that Thomas Covenant's actions serve their purposes.
The Dream Perspective
Thomas Covenant is a leper. Although he lies blameless in this, he hates both what he has become and what he was before his leprosy was diagnosed. In his dream, Lord Foul is a personification of the despite and contempt which Thomas Covenant's community feel for him.
In a way, Covenant can be seen as the creator, suddenly discovering in his mind the part of him that he hates. In order to overcome this problem, he has to face it and confront it. He realises that he craves an end to his impotence, both physically and mentally; but he also fears power: it can only be wielded at the cost of being stuck with the consequences of your actions. Guilt.
By overcoming the Despiser in the Land – or in his dream – Covenant accepts to use power and live with the consequences. In real life, he gradually accepts that he is guiltless of his leprosy and manages to stop hating himself.
The Workings of Despite
We all have a part we hate inside us. Lord Foul is here to convince us that we will never overcome it. Once he succeeds, we succumb to despair and think that the fight is useless. If we give up, he has won. In the Land, this happens time and time again. Sometimes it is so much the natural order of things that it seems that Lord Foul is at the root of all despair; other times, the machinations and manipulations are plain for all to see and yet unavoidable.
The first Lords of the Land realised that all their Earthpower (a sort of magic drawn from the fundamental nature of the Land) could not defeat Lord Foul; so they enacted the ritual of desecration which almost destroyed the Land and only succeeded in weakening Lord Foul. In their despair, they not only failed, but also hurt the Land, whose service they were dedicated to.
Later inhabitants of the land had an Oath of peace which they hoped would prevent them from repeating the ritual of desecration. But it also prevented their mastery of the earthpower equalling that of the Old Lords. It also gave them trouble fighting off Lord Foul's armies, which is why, to them, he is the Grey Slayer.
The giants call him Satansheart Soulcrusher. They are easily overcome: just showing them that evil exists and is sometimes concealed within themselves is an almighty blow. In his dealings with Saltheart Foamfollower, Lord Foul's chief strengths and weaknesses can be seen. Lord Foul's trap in Soaring Woodhelven seems to be aimed solely at Foamfollower, that he might be intimidated by his ability to wound others. But Foamfollower learns to accept the part of himself that hates and kills and proves to be Lord Foul's downfall at the end of the first chronicles.
To the Bloodguard, he is Corruption. Corruption of the Vow of service to the Lords which has made them ageless and sleepless for the past 2000 years. The sacrifice this servitude involves has served to increase their native strength of character. This prevents Lord Foul from being able to reach them. But it also exposes them to a great danger. They cannot accept the slightest flaw in themselves, so they have the hardest fall of all when they realise that they too are only human.
Lastly, the seduction of potency is the way that Lord Foul uses to manipulate Covenant. Covenant needs to use his ring if he is to defeat Lord Foul; but he is fundamentally scared of all forms of power. This is why Covenant believes that Lord Foul is also his inner Despiser. The one who laughs at lepers in the real world. So he decides to fight him, whatever the cost to himself, just because he has had enough.
So you see, unlike most other Bad Guys, Lord Foul is not only evil, but draws his strength from the evil hidden within every one of us. This self-searching pseudo-psychological perspective is a common trait in all of Stephen Donaldson's work.
Thus we become what we hate.