7. Mindless Hulk
The Hulk has always been attached to Bruce Banner, and in a way, they are one in the same character. Banner's anger fuels the transformation into the Hulk, and the angrier he gets, the greater the beast's strength. There isn't a known limit to his strength, and the Hulk has gotten pretty mad over the years.
Still, while the Hulk is attached to Bruce, there is some level of control, but when the two were separated, the Hulk became mindless. The so-called "Mindless Hulk" was the result of separating the two psyches, and without Banner to hold him back, the Hulk became all but unstoppable.
Without Banner's mind hanging out inside the Hulk's head, there was absolutely no control in terms of the level of the Hulk's strength. He became a beast without burden, and an already strong monster of a character became a truly unstoppable force.
Fortunately, it turned out that Hulk and Banner couldn't survive for long once separated, and while the Mindless Hulk achieved a level of strength few on this list could hope to attain, the two had to be rejoined eventually. When that happened, the Mindless Hulk became a thing of the past, but for a moment, he was the strongest being in the Marvel Universe.