8. Hulk (Bruce Banner) - 1643 points (28 first place votes)
The Incredible Hulk was created by Stan Lee and Jack Kirby as the ultimate Jekyll and Hyde tale. Scientist Bruce Banner is caught in an explosion of the gamma bomb he created, resulting in Banner becoming a violent, destructive green-skinned monster called the Hulk when Banner is stressed or becomes angry. The Army wishes to capture the Hulk, so Banner becomes a fugitive.
That basically was the plot of the book for many years, changed only really when Banner gained control for a time, and then, when writer Peter David began a long run, having Hulk become an enforcer for a Casino boss and then later, merging the various Hulk personalities into one cohesive "Professor Hulk," who joined a secret peacekeeping group called the Pantheon.
Ultimately, though, Hulk returns to, well, smashing. A few superheroes got tired of it, so they sent Hulk into outer space to settle on an uninhabited planet. That plan did not work, as the Hulk ended up on a warrior planet, which he eventually conquered. Finally content, the Hulk was married with a pregnant wife. Then the shuttle he was sent in exploded, killing his wife and most of the citizens of his capitol.
Now craving vengeance, the Hulk returned to Earth to avenge himself upon the heroes who sent him away. After the dust settled on THAT, a new Red Hulk was introduced that turned out to be Bruce's former father-in-law, Thunderbolt Ross.
More recently, after Bruce was shot in the head, Tony Stark used Extremis to cure the injury, but inadvertently created an intelligent Hulk, who in turn sort of went temporarily nuts. It is unclear what Bruce Banner's role will be in the Post-Secret Wars Marvel Universe. All we know is that there will be a NEW Hulk, Amadeus Cho (a young genius who was an ally of Banner for a time).
7. Thor (Odinson) - 1716 points (27 first place votes)
Created by Stan Lee, his brother Larry Lieber, and Jack Kirby, Thor is the Norse god of thunder, who was banished to Earth by his father to teach him humility, trapped in the frail human form of Dr. Donald Blake (whose nurse, Jane Foster, was in love with him).
However, soon, Blake found an enchanted cane which allowed him to transform into Thor, and Thor was a hero on Earth, using his god-like powers and his powerful magic hammer, Mjolnir, to fight the good fight.
Thor often visited his home in Asgard, and had adventures there, as well, mostly due to his evil half-brother, Loki.
Thor was a founding member of the Avengers, where he served for many years, including bailing them out more than a few times when things get out of hand...
More recently, some secret of Thor's past was revealed that suddenly made the Odinson unworthy of the name "Thor" and the power of Mjolnir. His old love, Jane Foster, has become the new Thor and the old Thor, now just calling himself Odinson, is using an axe he picked up from battle in Uncanny Avengers, instead. He also lost an arm in battle and has a fancy Asgardian prosthetic. We have yet to learn exactly WHY he became "unworthy." I'm sure we'll eventually find out during Jason Aaron's run on Thor.