graverobber9
ShinRa Guard
Yu Yevon is clearly the main villain. He invented the false religion of Yevon, selfishly created Dream Zanarkand by having many of his people self sacrifiice, and created Sin to solidify his power. Not only that but he is the one who REALLY controls Sin. Though Jecht might have "been" Sin, he only created the physical manifestation of it by being Braska's Final Aeon. Like Bahamut's fayth said, "Yu Yevon wears Sin (Jecht) like armor". Seymour was just a guy who was negatively affected by the repercussions of Yevonism (his mom became gave her life become a fayth) and lost his mind in result. He only worked in the storyline to show the party the corrupt and vile ways of Yevonism, which ultimately changed Yuna's mind regarding the Final Summoning (along with Tidus's and Rikku's insistence).