Akherontis
How do you define 'powerful'? Greek Mythology is not a videogame and tends to lack statistical attributes for its characters. And Zeus, Poseidon and Hades are not necessarily the most powerful gods, just the highest ranked. Even then, you have to consider deities like the Fates or Eros, so there's no real basis for comparison of power. The question is impossible to answer.
C/Khaos.... the void, the untouchable.
