I know I'm probably gonna take some fire for this but, Delita Heiral from Final Fantasy Tactics/ War of the Lions.
I know fans of the game say that he ended the War, became king, and eventually brought Ivalice to a time of peace, but he also lied, schemed, manipulated, and betrayed others to get to that point. He kidnaps the princess win over the Black Lion, earn the Princess's trust, and made ultimatum that guaranteed her dependency on him, killed Goltanna, betrayed the Church, and even use Ramza to defeat the Lucavi so that he wouldn't have to. Even his marriage to Ovelia is hinted to be part of his plan (he never mentions that he loves her; only that he'll protect her, which forced the Princess to depend on him for her own safety). Delita didn't even become King to make Ivalive a better place; he did so simply to prove a point: that one doesn't have to be highborn to ascend the social ladder. In other words, he became King simply for his own benefit, and not for the sake of others. I also see him as something of a medieval Charles Foster Kane: a man who, at first fights against the system, but eventually becomes the very system he opposed, a high-ranking nobleman whose path to top was made from those he deceived and betrayed.
What I love about Delita the most is that despite everything he's done, he gets away with it: he becomes King, united Ivalice under his rule, and ushered it into an time of peace with his deed ultimately being glorified for years too come. I'm honestly a sucker for those types of villains, as they're rarely ever seen in modern games (unless I missed some). Even after a decade of playing the game, Delita is still one of my favorite villains.