He may be the most powerful in the FF7 series, but not in the entire series. I believe Kefka and Kuja are better. Kefka has eight dragons, a beam of light that can kill you from any point in the world, and when he's in the area of the Goddess statues, he can't be hurt. When Kuja achieved Trance, he destroyed an entire world, and he controls the Mist, and can conjure up strong Mist monsters.

Beat that, mama's boy!