if I am going to make a character with a sinister plot I perfer to have them truly in their heart think they are trying to complete some goal the completely wrong way.

like my charcter Kryson, who I honestly say if he were real I'd date him. He was a dark paladin type guy. Believed he could accomplish anything there brute force and manipulation of people around him. Had no issues with using people then killing them if they had nothing left to offer him.

His goal really was a good one, he wanted to end the enslavement of his race (humans) to elves he also accomplished it then make his country into a super power so that no one would harm it again. Also noble, just he had to do it threw taking all the power for himself and leaving none for anyone else. He was a fun character to play.

Now how he got that way I'm not sure, I just kinda started playing him as power hungry madman at first and it just kinda evolved into that.

I hope that answers the question, I generally try to explain why my characters are the way they are but usually I have to play them and get into thier heads before I know for sure.