5 people to save the world.

[Jakensama]

There is a comic called Hulk: The End where he is the last living person on earth because of nuclear war. The only other life left are these huge cockroaches that eat everything, so they keep eating him down to the bones and he keeps regenerating. He's pretty much invincible.

Hulk probably wouldn't lift a finger to save the world though, he doesn't care, he just wants to be left alone.