As the two of the strongest characters in Marvel Comics, the Thing and the Hulk have a long-standing rivalry with a history of fights stretch back to the original Fantastic Four #12. While the Green Goliath and sweet Aunt Petunia's nephew have gotten the best of one another once or twice throughout the years, one version of the Thing was strong enough to defeat the Hulk twice, each one from a different dimension. In the Ultimate Marvel universe, Ben Grimm of the famous Fantastic Four may not be the prettiest but he's definitely one of the strongest heroes out there.
The first battle occurred in the Ultimate Fantastic Four 'Crossover' storyline by Mark Millar and Greg Land where Sue, Johnny, and Ben travel to an alien dimension, later known as the Marvel Zombies world, to rescue Reed Richards after incapacitating their undead doppelgangers. Smashing and burning a path through the hungry zombie superheroes, the Four and their small group of survivors are blocked by the landing of a zombified and starving Hulk. Brushing aside the other Magneto's help, Ben steps up having always wondered if he'd be able to defeat the infamous member of the Ultimates known for his strength and temper. This battle was over quicker than it began as the Thing was able to knock out the Hulk with one punch, his question answered as they headed to the Baxter Building so they could return home.
Ben would later get his wish to face his universe's version of the Hulk in the Ultimate Power series which served as a crossover between the Ultimate Marvel and the Squadron Supreme universes. In the issues by Jeph Loeb and Greg Land, the Hulk was revealed to be a secret weapon set in motion by Nick Fury, to help swing the battle between universes in his favor.
His chaperone Spider-Man was barely able to keep the Hulk in line as the Ultimate heroes and the Squadron Supreme finally worked together to stop the uncontrollable and hungry Hulk. Already frustrated that the current events happened over Reed Richard's desire to find a cure for Ben's condition, the Thing took a stand and fought the Hulk, again. While he acknowledged that the Hulk was most likely stronger than him, the Thing stated that he was the better man due to the strength of his heart. While the Hulk furiously declared he would eat Thing's heart, Spider-Man and Invisible Woman had heard enough and helped Ben by webbing Hulk's face and then projecting a forcefield around his head. Distracted and dizzy, it gave Ben the perfect opportunity to once again knock out the Hulk with a single punch, calling the unconscious grey giant a jerk and saying this town wasn't big enough for the two of them.
In the mainstream Marvel universe, the Hulk and the Thing have had a back and forth for years, with the occasional victory fueling the debate of who is stronger. The current Fantastic Four series apparently settled it once and for all in Fantastic Four #13, when Ben Grimm took a page from his Ultimate counterpart and knocked out the immortal Hulk in one devastating punch. While fans of either hero will continue to debate and provide evidence to support their claims, one thing is for sure in the Ultimate Marvel universe, Ben Grimm aka the Thing is truly the strongest one there is, humbling any Hulk he comes across who says otherwise.