Topic: Game Villains with the Best Story Buildup?

There are pretty much two types of game villains.One, those who pretty much stay put in their layer the entire time (looking at you Ganon), waiting for you to become their equal before confronting you. Two, those who are confident in their destructive power, and often show up throughout the game to cause utter destruction in front of you, or beat the tar out of your underdeveloped hero, just because you're too weak to do anything about it (making that final battle feel all the more rewarding, knowing you built up to such power). Here are my favorites of the latter kind (cautious, there will be spoilers):

3. The One King (Suikoden Tierkries) - Throughout the game, you hear tales of The One Hing, whom has destroyed hundreds of worlds without anyone discovering how to even slightly injure him. It's real nerve wracking, knowing he's going to come to your world eventually, with no idea as to how to even give him a scratch (you're in a mideaval world, but it's made clear that The One King effortlessly destroyed a much more advanced civilization, described as if he had obliterated our modern world).

2. SA-X (Metroid: Fusion) - This name should ring a few bells here. There's nothing more nerve wracking than wandering around as an underpowered Samus, knowing that a fully powered copy of yourself could pop up at any moment to destroy you with a few quick blows, and your only options are to hide and/or run like h*ll.

1. SIN (Final Fantasy X) - You confront SIN many times throughout this game, with your efforts to stop it being equivalent to a bee sting. In fact it's so powerful, it destroy's two cities & wipes out an entire army, rendering all your efforts mute. The final battle is equally epic in showing it's power, with a multi stage confrontation that includes an airship assault, as well as your party climbing on & inside it to achieve victory, destroying it piece by piece.

(spoilers end)

Metal Face (Xenoblade chronicles) - Spoilers throughout the game, metal face does whatever he can to piss you off, such as killing fiora, and taunting you. He spends the first parts of the game beating the crap out of you whenever he finds you, and whenever he gets slightly injured, he is forced to retreat. You go about the game realizing that there are other faces, but metal face must be special, as he has a unique design. When you near the final confrontaions with him, you discover not only is he not alone, but there are many more special faces more powerful than him. spoilers end here

Kefka Final Fantasy III (VI) - Kefka does everthing in his way to get at you from poising the waters of a castle to burning down another to chasing you through a laboratory that you have no clue where he is at till you hear his famous laugh. On top that he destroys the world. It isn't till the final battle that he becomes a god that you are able to finally get back at him. Yeah you know that he is an all powerful wacked out general but who would have thought that a god he would become.

Bowser. First he shows up and kidnaps your girlfriend. Then you run after him! And apparently that motive is enough to attempt killing him over and over.

The tension rises every time you throw him into a pit of lava. All the foreshadowing towards the final encounter, it's almost too much to handle. Then when you finally throw him into that last pit of lava, which must somehow be different from the other lava pits, it's the most rewarding thing to watch him burn up and turn into ashes. Unless it's those boring mario games, where he pretends to renounce his evil ways and mario just goes along with it, as if Bowser ever tells the truth.

I came here to say Metal Face from Xenoblade Chronicles, but @Happy_Mask beat me too it!

My second choice would be GLaDOS from the Portal series. I don't think she really needs any elaboration as to why I chose her.