4. Ion (DC Comics)
Ion isn't actually a character per se, it's actually a benevolent symbiote, created when the first act of willpower in the universe was carried out, which embodies willpower itself and is the driving force behind the Green Lantern Corps and their power rings. When the entity has a host, the name Ion is often used as an alias by the hosting character - and in this case I'll be referring to the time the Green Lantern Kyle Rayner was its host. Of course, any character hosting Ion has all the usual powers of a Green Lantern (flight, incredibly durable automatic forcefields, energy manipulation, the ability to create constructs and the ability to augment their own physical statistics etc), but they also possess other abilities of untold power. As Ion, Kyle Rayner was completely omniscient and omnipotent, possessing all knowledge and able to exist everywhere at once. He had complete control over time, space and reality and was essentially God. He fixed all of the world's major problems at the same time by virtue of being everywhere he was needed simultaneously. He was never defeated and chose to submit his powers and bled them off to avoid losing his humanity. He did so by creating a generation of Guardians and restarting the central power battery - both of which are fine indications of the level of power he possessed, given that the Guardians are insanely powerful beings and the central power battery is what powers every single Green Lantern ring (of which there are hundreds).