This is a topic I see argued over a lot. The candidates are usually Yu Yevon, Sin/Jecht, Seymour or the Yevon religion.

Who do you think and why?

I think it's the Yevon Religion. Basically they are the reason why Sin had been around for so long, why people wouldn't even dare to think that there might something more to the world other than what Yevon Presents them. Seymour is just a representative of Yevon but I wouldn't call him the villian. I mean if you think about it, everything is related to the Yevon religion. Yu Yevon, Sin, Seymour, everyone. That's pretty much who or more to the point what is the main villain in this game.

Tidus is the villain because of his laugh. (full stop)

My money's on Yunalesca. All that time while being an unsent she kept fooling every summoner that the only the final summoning is the only way to defeat Sin, thus letting the circle continue.

I thought it was Yu-Yevon, since it was manipulating things from behind the scenes through Sin.

For me, I would say the Yevon religion. Before I get into that, I'm going to address the other candidates as to why I didn't choose them:

- I never thought that Yunalesca was the main antagonist because she just created the Final Aeon and passed on the Final Summoning to worthy summoners. If anything, I think that Yunalesca thought that the Final Summoning was the only way to have some ''resting time''; and the only weapon to wield against Sin. In the end, I felt that Yunalesca allowed Yuna to make the choice of choosing to complete her pilgrimage or not.

She was a hell of a fight but I view that the group did attack Yunalesca.

- I didn't think that Seymour was the main villain because he was a little lame. He was just power-hungry. Even if his plan of becomming Sin (towards the end of the game) came through, I doubt he would have much control; Yu-Yevon controls Sin.

- I don't think that Yu-Yevon/Sin/Jecht was the main villain because Yu-Yevon/Sin was created 1000 years back during the war with Zanarkand. This might be my science classes comming into play =P but I feel that Yu-Yevon/Sin was just at the top of the food chain and the humes were just stuck at the bottom.

I do think that the Yevon religion was the main antagonist of the game because the Yevon religion taught that only the Final Summoning is their weapon against Sin; and that the only way to defeat Sin forever is to atone for the Sins from the past. Of course the Yevon religion betrays itself by using Machina in Bevelle and the judgement scene with Yuna is also another example of Yevon's betrayal.

Anyways my point is that the Yevon religion got so caught up in their teachings, that they made people feel that there was no other option to defeating Sin other that atoning and the Final Summoning. The Yevon religion made the people of Spira do nothing about legitimately killing Yu-Yevon/Sin forever since it brainwashed everybody. And the Yevon religion also reinforced hostile attitudes towards people who believed differently (the example of this is the attitudes towards the Al-Bhed).

You still didn't disprove my theory!

I thought it was Yu-Yevon, since it was manipulating things from behind the scenes through Sin.

I agree with this, Yu Yevon seemed to be at the heart of Spira's problems. Without Yu there wouldn't be a Sin/ Yevon religion.

Yu Yevon. This whole mess started because of him. While it is true he lost control of Sin, he was the one who initially created it.

The Catholic Church, erm...I mean...Yevon Religion?

I'm the main villain.