There's two main antagonists, Seymour and Jecht. Just like there's two protagonists, Yuna and Tidus.

Since there's two different protagonists, each has their own antagonist as well: Jecht for Tidus and Seymour for Yuna.

Yu Yevon, and the religion born from it, is the main villain, not antagonist. I have no idea how many times I've said this.

This question has been asked before Shuyin knows how many times, I myself having asking it following by a post explaining my position (aka what I just said) long time ago. Also, it's not exactly a pop quiz if there's no 100% correct answer, or am I the only one who thinks that? Welp, guess I can't vote.

That's what makes FFX so great and distinguishable.

I love Seymour I mean is supposed gonna be final boss instant yu yevon or jecht ( imagine )

Transformers look cool and also voice too

I mean look this design , Seymour reference all antagonist Final Fantasy series such sephiroth , kuja, caius and other

In Dissidia Final Fantasy, there supposed Seymour appear instant jecht according squere Enix

@CorujinhaGamer26 is pop quiz, there s familiar question talk about who antagonist in FFX, people choosing yu yevon, but that was wrong I m gonna choose jecht

Jecht of course is antagonist in FFX

If you take it purely by the meaning of the word antagonist, then seymour is the antagonist. He litteraly is the person who goes against the heroes. Jecht is deuteragonist and more of a pawn in the grand scheme or in soms view the object for Tidus to drive him. I nearly want to say that Jecht is more on the protagonist side due to his role in the story.

Yu yevon is the concept of evil in the world and the driving force of the antagonist.