Happy 50th Birthday, Avengers and X-Men!

The Avengers Comic Art - P 2013
<p>The Avengers Comic Art - P 2013</p>   |   David Finch/Marvel Entertainment
September 10, 1963, saw the debut of not only Marvel's first Avengers comic, but also the publisher's X-Men.

Throughout the 1970s, each issue of Marvel's Avengers comic featured an introduction that started: "And there came a day, a day unlike any other, when Earth's mightiest heroes and heroines found themselves united against a common threat." Fifty years ago today -- September 10, 1963 -- was that very day: the official publication date for not only Avengers #1, but also X-Men #1, both super-teams the product of a collaboration between Stan Lee and Jack Kirby.

Both teams had their roots in earlier collaborations between the two, who were already working on Fantastic Four and Thor, among other strips. That's most obvious with Avengers, which brought together characters from their other work into one series. X-Men, meanwhile, mixes the group dynamics of Fantastic Four -- complete with group uniforms -- with the teen soap operatics of Lee's Spider-Man collaboration with Steve Ditko, one of Marvel's rare non-Kirby-inspired smashes at the time.

Interestingly enough, neither book really hit its groove immediately. Avengers lacked a crucial piece of its DNA until the fourth issue of the series revived Captain America, who ultimately became the character around whom the team would revolve for the next five decades. Its original lineup was replaced with new characters less than two years into its run, setting in motion a tradition of forever-shifting memberships and covers announcing that "the old order changeth!"

X-Men, meanwhile, went through multiple incarnations during its first years -- including the death of Professor Xavier (don't worry, it didn't stick) and breakup of the team -- ending in the essential cancellation of the series in 1969, with #66 of the series being the last nonreprint material to appear in the title until 1975's #94. By that point, Len Wein and Dave Cockrum had created the "All-New, All-Different" X-Men, which featured an entirely different cast, including Wolverine and Storm. It was this second version of the team that found favor with comic book fandom (Marvel can thank longtime writer Chris Claremont for that; he wrote the X-Men series and multiple spin-offs for 17 years without break).

While X-Men became increasingly successful and, as a result, important to Marvel's fortunes -- the addition of titles such as New Mutants, X-Factor, Excalibur and Wolverine demonstrating the strength of the brand -- the Avengers franchise stayed in the background somewhat until 2004, when rising star writer Brian Michael Bendis reinvented the concept behind the team with his New Avengers series.

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In New Avengers, many familiar faces in the team were replaced by a new lineup that included some of the publisher's biggest names, such as Spider-Man and Wolverine. It was a move that engendered much derision from long-term fans, but increased sales and a renewed importance to the Marvel line as a whole thanks to central roles in annual events like Civil War, Secret Invasion and Siege couldn't be denied. Avengers had become Marvel's most important comic book -- Earth's mightiest heroes, at least in terms of sales figures in the Marvel stratosphere.

The competition between the two teams has been mirrored across different media too. X-Men got to cartoons and movies first, but it was Avengers that ultimately had a bigger impact in both, with Marvel's The Avengers and Avengers Assemble becoming Marvel's flagship movie and animation properties -- at least until next year's X-Men: Days of Future Past, which might offer everything necessary to put the X-Men back on top.

In 2013, the X-Men and Avengers characters have both grown significantly from their original incarnations, in ways that are both unrecognizable and entirely fitting with their basic concepts. The X-Men are still fighting against prejudice and at odds with the authorities as they do so, and the Avengers are still saving the world from threats bigger than any one superhero could handle, 50 years after they first appeared on the scene. Fifty years from now, they'll likely be doing the same thing somewhere, in some media we haven't imagined yet. Happy birthday, superheroes. Thanks for keeping us alive all these years.