In my book The missing peace council One of my characters,Lord Bladen Krest turn against the group and then go evil again. I need some help on this. He has a great history and i want it to slip into him becoming evil and then good again. 

  Maybe it would help to try thinking a little less about how good or evil the guy is, and just let him drive his destiny. He is the character doing all these things, after all.

THat would work wont it. Alright thank you.

I guess it it is important first of all to see evil and good as a continuum rather than a static alignment. For realism it is necessary to explore the character's motivations for the way he behaves and then carefully detail the event(s) that lead him/her to change his outlook on his/her own behavior. No one wakes up and says "I think I' going to be evil today" and very often, those who are percieved by others as evil see themselves as justified and seek to explain the necessity or extenuating circumstances leading to their "evil" behavior.

Making a good villan is one of writings challenges.

I always find that to create a character that you want people to percieve as the "bad guy" the majority of the work goes before you actually introduce your character.

Take Hannable Lector for example. Before you even meet him you're told stories of his behaviour, he's locked in an assylum, Starling has a claustrophobic elevator ride down to see him where she's shown a picture of a nurse he disfigured and how calm he was when he did it. She has to go through multiple gates and walk solitary down a long character of crazies before she see's him standing perfectly still and presentable in the middle of his cell. Yet he is polite and courteous. The whole scene of Lectors introduction is unsettling which reinforces the characterisation of him as the villan.

Because of the effort made in presenting this character, Lector made up less than 20 minutes of the movie, but stole the show. In the book Thomas Harris has more time to work on the character, but the end result was the same.

An evil character is one that the protagonist is fearful of yet must defeat. A strong characterisation will mean a lot to your story, but an archetypal villan has one very basic rule to follow. They must oppose that which your protagonist stands for.

I'd say think of the villans you've admired most in books and movies and see how they were represented. What was it that made them appear "evil" and keep that message reinforced in the character for the duration.

Villans are always more theatrical than heroes, so where a hero must prove their virtue to an audience, the villan can be built in imagery and emotion before they ever reveal themselves to the audience. Don't forget the old horror axiom, "its not what you show, its what you don't show".

if they like causing pain, (emotional, mental, or physical) that sometimes makes them even worse. especially if they're the type of villain who finds out a person's mental or emotional weakness and then exploits it ruthlessly. especially if they do it in such a way that their victim doesn't know what's happening, the victim might even like the villain, and the villain might be kind to the victim. the villain would gain the trust of the victim, then use that trust to undermine the victim's security, sense of self, ego, life, whatever. that sort of thing makes the villain a bit creepy and really really hateable

I love the way that riddlerose put that, but don't forget, that the audience doesn't have to know what you know.

If your chapter opens: "His eyes let in the little shards of sunlight that darted through the break in the blinds, but even as he woke he couldn't help but remember the dream that he had Joe exactly where he wanted him. So long he'd wanted him where he had him now, and even the apparently delightful ray of sunshine that had started his day would stop him from what he had fixed in his mind now." Joe is clearly the protagonist, but its the antagonist that we are feeling for here. Make him hate things the audience will love, I've kept is basic, he hate ssunlight, but you can see my point. Paint a picture. Riddlerose hit the nail on the head when she (I assume she) defined it as the villan and victim. These roles are immensely important when you're planning your villan. (I apologise if I keep going on about this, but I love writing villans, bad guys are always so much more fun to write for!)

Also again, the best villians are 3 dimentional. i.e they sound like real people with real human motivations for the bad things they do. I think these tend to be a bit more interesting than the "Mwahahahah I'm doin EVIL!" variety.

heh yeah... that kind usually comes across as kind of silly... XD

That kind is usually only in parodies these days.

Well, I'll amend your thought to say that is only used EFFECTIVELY as parody these days. There are still a number of weak stories and movies in particular that have really weak villians. Go watch any generic horror movie for example.