When the Hulk guest-starred in Jack Kirby and Stan Lee's Fantastic Four #12, it was the first time Marvel's heroes had crossed over at all (it came out just before “Amazing Spider-Man” #1, which also featured a hero crossover). However, while there was a small skirmish in that issue, the fight everyone wanted to see – the super strong Thing versus the super strong Hulk – did not happen until the twenty-fifth issue of the “Fantastic Four.”
In the issue, the Hulk is on the run, like normal, when he discovers that he has been replaced on the Avengers by Captain America. He determines he will travel to New York City to destroy the Avengers.
Once in New York, the Human Torch tries to slow the Hulk down, but he is no match for the Hulk. Mr. Fantastic had just come down with an illness and while the Thing and the Invisible Girl wanted to stay with him, he insisted that it was more important that they try to stop the rampaging Hulk.
Once in battle, Sue's force field proved no match for the Hulk, and she and Johnny were taken out of the fight, leaving the match Marvel fans had been waiting for – the Hulk versus the Thing!
Their fight takes up the rest of “Fantastic Four” #25 and a large chunk of issue #26, as well! Right from the get-go, the Thing realizes he is in real trouble as the Hulk is a great deal stronger than expected. In addition, this was during a time period where the Hulk was no dummy, so in fact, he was the one often coming up with crafty ways to fight his opponents, which meant even worse trouble for the Thing!
Practically the whole fight is done in pages with five, six and sometimes even seven panels per page, allowing Kirby to draw a very long fight in just a few pages. The Thing uses everything he can think of, but the Hulk not only shrugs it off, but goes on the offensive against the Thing. For the first time that he can recall, the Thing is on the defensive from an opponent.
At the end of the issue, the Thing appears down for the count. He even notes that maybe this is good for him, as he had begun to think he was unbeatable and the Hulk helped show him that was not the case. Still, he slowly rises from his injuries and evokes a now familiar name for the first time in the comic book, "Well, like my dear ol' Aunt Petunia used to say... 'you can only die once!' And that's the only way he'll stop me now... by killin' me!!"
In the next issue, the Hulk does not kill the Thing, but nor does the Thing fare any better. Eventually, the Avengers show up and they have their share of problems with the Hulk, too. Ultimately, the issue ends in an anti-climax, as during one of the fights the Hulk is thrown nearby water where he transforms back into Bruce Banner and floats away. The Avengers and Thing leave not knowing if they could have defeated the Hulk, but they should feel good knowing that they would encounter him again. In fact, the Thing/Hulk match-up would present itself many more times over the next forty plus years.