The Hulk
Robert Bruce Banner - saved a boy named Rick Jones from a gamma bomb test and was exposed to the blast. The gamma radiation transformed him into The Incredible Hulk. The angier the Hulk gets the stronger he becomes. Different transformations have been seen as the Hulk, including a Grey Hulk, the Savage Hulk, the Professor Hulk, etc. These Hulks are possibly outward manifestations of Bruce's inner psyche according to Doctor Samson.
I've fought against the Hulk and alongside him. He is one of the strongest beings in the Marvel Universe. And, with his anger, there is a theoretical possiblity that there is no limit to his strength. He is quite possibly the "strongest one there is."
