Arguably Sauron. He was absolutely correct in his intention that no being, no matter elf, man, dwarf, hobbit, or even Maiar (essentially angels) could resist the Rings power. And he knew the Valar (essentially gods with a small g) wouldn't intervene like they did at the end of the First Age. Not to mention he corrupted the other Rings of Power during their creation, except for the Elven three, but it didn't matter; the power he imbued the Ring with ensured they would all answer to him. They would succumb, and even if they "overthrew" him, his life force was bound to the Ring, and as long as it exists he still wins.
Shame about that whole hand of Eru/Gollum/pit of fire thing that got in the way.