Thor: Ragnarok has brought one of Marvel's biggest grudge matches into the spotlight by pitting the god of thunder against the Hulk in a literal gladiatorial bout. It's only the second time the two have met as opponents in the Marvel Cinematic Universe, but it's the latest entry in a long, long list of fights in... well, just about every other medium. The question is: why?
Why are Thor and Hulk at each other's throats so often? When did it start, and why does it matter? To answer these questions, we have to go back -- way back.
The Early Years
Hulk and Thor's first proper fight occurred in 1965's Journey Into Mystery #112, a battle that would wind up being prophetic for more than one reason. In the issue, a literal group of school children pose the question to Thor about whether he or Hulk was stronger.
Now, Journey into Mystery is Thor's home turf, so the story is appropriately Thor-focused as he recounts a tale about his last "encounter" with Hulk where he chose to go toe-to-toe with him without the aid of Mjolnir, but with all his godly strength intact, thanks to a deal from Odin. The issue ends without a clear winner, but the seed of the idea had been planted in the hearts and minds of every kid reading comics in the mid-'60s.
This was the height of the Silver Age of comics, where the Comics Code and the "imaginary story" (read: non-canonical) were in their heyday; when comics readers of all ages were most primed for the hypothetical and the bizarre. And with the growing strength of Marvel's shared universe getting stronger by the issue, the "who would win?" hypotheticals were reaching a fever pitch just about everywhere. But there was one small problem -- the hypotheticals, combined with that same shared universe, often set precedents that creators and editors would then have to (at least, halfheartedly) maintain. This meant that actually giving definitive answers was a dangerous move -- so the earliest conflicts were vague out of necessity than any sort of genuine, merit-based, behind the scenes arithmetic.
Be that as it may, the fact that there was no real definitive answer in these fights was setting a sort of precedent all it's own -- the endless "who is the strongest Avenger?" debate took on the same circular logic as the "immovable force" versus "unstoppable object" question, maybe more so than any other set of superheroes at the time.
The problem was, both Thor and Hulk had abilities and strength levels that were so vaguely defined that there were no clear caveats or addendums that could be assigned to either side of the argument. Unlike characters like Iron Man, who depended on the level of tech he had available, or Captain America, whose effectiveness was contingent on the (superheroic) human body, Thor and Hulk both existed in the realm of extreme hyperbole by default, and therefore, were much less easy to construct a real case for.
How strong can Hulk get? How much can a literal god withstand? Who knows? Who decides? Needless to say, the kids of the mid-1960s were enthralled.