I'm really trying not to let Marvel Comics dominate the choices here, but there can be little question that no prior comics company had ever promoted the crossover with such outstanding verve and inventiveness. There were some crossovers that were ploddingly ordinary, as with the FF/X-men meeting in FANTASTIC FOUR #28, and some that made you scratch your head in bewilderment, as when Iron Man met Angel doing a solo from the X-Men book in TALES OF SUSPENSE #49.
But if I had to choose just one to represent Marvel at its best, it would be the two-part crossover of the Fantastic Four, the Avengers, and the Incredible Hulk in FANTASTIC FOUR #25-26.
The first part of the story is the one that has gone down in comics-fan history. The super-foursome had encountered the Hulk in a previous issue of their magazine, but this meeting proved something less than stellar. Possibly both Lee and Kirby felt the same way, though one should not overlook the likelihood that the Hulk's peripatetic guest-appearances after his series' cancellation were aimed at drumming up fan-support for the character's next series.
Issue #25 has become legendary for one of Jack Kirby's most superlative scenes of two brutes tearing apart a city:
Yet Kirby never stints on the "ordinary human" elements in the mix. We see police frantically cordoning off the battle-areas, physicians battling to preserve lives-- among them, that of the gravely ill Reed Richards-- and the Thing's personal pest-brigade, the Yancy Street Boys, intefering with the big battle in comedic fashion. Kirby doesn't just tear down a generic cityscape: there's a definite sense of place to all of the boroughs through which the two monsters rampage.
The plot doesn't require much summation. In one of Marvel's early attempts to carry over parallel events in "real time," Lee and Kirby picked up on an ongoing plotline from the AVENGERS title-- the heroes are continually scouting about for their rogue member, the Hulk, to prevent the hostile behemoth from hurting anyone. While the Avengers are Hulk-hunting in the green giant's usual stomping-grounds down Arizona way, the Hulk happens to read about how he's been replaced in the group by the reborn Captain America. The monster gets a mad on to take on his old partners again, and heads for New York. Not only are the Fantastic Four the only heroes available to fight Old Greenskin, three of them are sidelined rather quickly for one reason or another, so that the Thing is free to take on his fellow muscle-bound monster for several pages of rousing chaos. Significantly, the Thing finally loses the fight against his larger opponent: an illustration of the classic aphorism: "a good big man can always beat a good little man." But Lee and Kirby don't allow the heroic Thing to throw in the towel despite his defeat, and the battle is renewed in #26.
If Part One was meant to push the Hulk closer toward a new series, Part Two spotlights the ongoing AVENGERS feature. "The Avengers Take Over" doesn't have nearly the same pulse-pounding momentum as "The Thing vs. the Hulk," and there's a subtle shift in the storyline as apparently both Lee and Kirby forgot the Hulk's original mission. Initially the Hulk wanted to beat up/kill the Avengers for having replaced him in the group with a newcomer-- a motivation that didn't make any sense, given that Greenskin was the one who departed the group back in AVENGERS #2, of his own free will. In Part Two, the Hulk is suddenly irate at camp-follower Rick Jones because he used to be the Hulk's old sidekick, and now he's started hanging around Captain America. This didn't make much more sense as a rational motivation. But the idea of Hulk simply being jealous that his old buddy had a newer, handsomer friend resonates with the original fantasy behind the Hulk's literary predecessor, as the "Mister Hyde" in him sought to avenge wounds suffered by Bruce "Jekyll" Banner.
The inking by George Bell (aka George Roussos) is the story's greatest deficit: the former BATMAN inker never proved a good match to Kirby's pencils at the best of times. There are gaffes in continuity as well: during a scene that takes the two monster-opponents into the Hudson River, the Thing flees the Hulk in a motorboat-- and the Hulk chases after by leaping along the waves of the Hudson. And even as a kid, I had to wonder at the ending: the Hulk falls into another body of water, transforms back to Bruce Banner, and simply floats away-- apparently protected by an authorial providence that made sure he didn't just drown.
Still, to repeat myself egregiously-- more than the Galactus Trilogy, the Master Planner saga, or any other touchstone, this is Sixties Marvel at its best, with or without crossovers.