While Thor has long been irritated by the fact that he's technically not the strongest Avenger, he at least got to claim that title for a little while when he combined his power with the Hulk's, assuming a staggering new form.
The transformation took place as part of the 'World War Hulks' story, in which the Red Hulk's storehouse of stolen power was distributed among Marvel's heroes, causing them to Hulk-out and assume gigantic new forms that unlocked the full extent of their powers. But while heroes like Ms. Marvel, Cyclops, and the Human Torch all got god-tier upgrades, the strongest among them was Thor Odinson, whose control of his diving lightning only increased along with his muscles.
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In Jeph Loeb and Ed McGuinness' Hulk #21, Red Hulk (aka General 'Thunderbolt' Ross) falls afoul of his former allies in the Intelligencia. This group of Marvel's smartest villains — including MODOK, the Leader, and the Mad Thinker — intend to take over the US, siphoning off Red Hulk's collected energy and using it to empower a new army of Hulks. Thankfully, several Marvel heroes are also affected, inheriting the traditional lack of emotional regulation that characterizes Hulks, but capable of pushing through the fog of rage to hold back the Intelligencia's army. Each hero assumes a towering form, but with the drawback that the incredible power will burn out their bodies in twenty-four hours.
After Thor beats down the Red Hulk, he teams up with Spider-Man to battle the Intelligencia's army, but gets distracted trying to control the Hulked-out Peter Parker. In World War Hulks: Spider-Man vs Thor's main storyline (from Kieron Gillen, Jorge Molina, Paul
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