With "Doom" recently rebooted, I think it is a good time to remind everyone who the most powerful fictional human to ever be conceived is: Doomguy. Warning: This article contains spoilers for all of the "Doom" games, so be warned!
That's right, this mean, green space marine is more powerful than Gandalf, Thor and even Master Chief who commands space marines to fight against space zombies. For the first "Doom" game that came out back in 1993, the premise was that Doomguy was the only surviving marine after the gates of Hell open on Mars' two moons, Deimos and Phobos.
By saying he is the only surviving marine is only somewhat true because many of his comrades were possessed and now attack the Doomguy on sight. This poor guy not only has to survive on the Moons, he also has to destroy his possessed friends and co-workers, as well. To make matters worse, the only way off the moon is on a shuttle that he does not know how to pilot, so he must continue forth into the unknown. As he progresses, he eventually finds himself in Hell and ends up in the city of Dis, which is made up of the sixth through ninth levels of Hell, and battles a demon that looks like a brain on stilts.
As he fights to hell and back, Doomguy eventually makes his way to a portal the demons use to enter Earth, which is swarming with hellions that he has to exterminate, only to find that Earth, itself, is almost completely in ruins and humanity trying to escape. After fighting through vicious hordes and shutting down a device that was preventing humans from leaving Earth, which an entire army couldn't do, he has to make his way back into Hell to stop the invasion. Once in Hell, the only way he can seal the portal is by killing the Icon of Sin. I'd like to see Gandalf try to do that!
Did he succeed in sealing off the gates of Hell from invading the Earth and destroying mankind? Mostly. It turned out that a single demon survived on a satellite orbiting Earth, and since he has dealt with demons before, he would be the perfect guy for the job! Spoiler: He kills that demon, too. "Doom 3" is ambiguous on whether it is a reboot or a sequel, but if it's a sequel, then it just adds another level of awesomeness on Doomguy's part. "Doom 3 has a demon dragon in it."
This guy not only goes to Hell, but he comes back and then goes back a second and possibly third time! Many other characters who die are usually only resurrected once, but Doomguy doesn't even die, yet he comes back from the afterlife twice and still keeps fighting! The craziest part about all of this is that he does this all alone.