Justice League of America and The Avengers are where DC and Marvel Comics keep their most expensive toys: DC has Superman, Batman, Wonder Woman and many others, while Marvel has Ant-Man, Hawkguy and ... uh, Jann of the Jungle, I think? There might be a couple more. Obviously, the very idea of putting both teams together is enough to make fanboys and accountants alike cream their pants, which is why the companies decided to make it happen in 1983. However, editorial disputes and the sheer logistics of getting so many trademarked logos on the same page caused massive delays, and the crossover only came out in 2003, in a vastly different form.

DC/Marvel
All the other superheroes were dead that month, so Superman had to fill in for them.

But wouldn't it be awesome if the writers had said "f**k it, let's do a crossover without telling our bosses"? Yes, it would, and we know this because it happened a bunch of times in the '70s -- The Avengers and the JLA would "coincidentally" fight obvious copycats of the other team on the same month, or a story that started in an issue of DC's Aquaman would sneakily continue in Marvel's Sub-Mariner. This was possible due to two reasons: 1) the publishers didn't always bother to read the books back then (especially the "guy who talks to fish" ones), and 2) while the companies hated each other, the creators were all pals and would sometimes party together. In fact, the best example of a secret crossover involves the writers doing exactly that inside the comics.

In 1972, DC writer Len Wein and two of his Marvel counterparts were hanging out at the Rutland Halloween Parade in Vermont when they realized that place would make the perfect setting for a superhero crossover, since everyone was already dressed in ridiculous (and potentially copyright-infringing) costumes.

via Comics Alliance
Really? Your name is Marv Wolfman and that's who you dress up as?

So they did that. In Marvel's Amazing Adventures #16, we see the three writers driving to a party in Rutland when they run into Beast of the X-Men (whom they fail to recognize, despite getting paid to write his comics).

Marvel
"No, Batman, come back! I have so many questions!"

After many misadventures, the writers are seen reaching the party in DC's Justice League of America #103, only for their crappy car to get hijacked by a wizard who was just fighting the JLA. Also, Len Wein's wife is temporarily transformed into Supergirl.

DC Comics
"I had a nightmare about Superman saying we had to play husband and wife, even though we were cousins."

And finally, in Marvel's Mighty Thor #207, they witness Loki falling off a cliff while they run after the hijacked car. Note that Wein's wife is still wearing the Supergirl costume:

Marvel
The guy in blue keeps stress-puking, which is why he's changed his shirt three times today.

Despite the fact that the idea was 100 percent unofficial and unsanctioned, the writers even found a way to get the biggest characters from both companies to "appear together" in the same panel. In DC's side of the story, the Justice League agrees to help out with the Rutland parade -- the same parade that's seen again in the Thor issue, complete with the real Superman and Batman standing in the background.

Marvel/DC
Spider-Man isn't completely sure if he's DC or Marvel, so he's covering his bases.

Meanwhile, millions of people were probably getting slaughtered by aliens in New York because all the superheroes were partying in Vermont, but it was totally worth it.

Howard the Duck was created by Marvel Comics writer Steve Gerber in 1973, but then Gerber quit the company and had to witness his character being put through a series of indignities -- not the least of which was this (NSFW? I guess?) clip:

Also, the rest of that hideous movie. Believe it or not, Howard continued appearing in comics after that, and Marvel occasionally invited his creator to write him again ... an opening that Gerber used for some sweet, sweet revenge.

While Gerber was suing Marvel over Howard's ownership in the early '80s, he co-created a character called Destroyer Duck with Jack Kirby, a.k.a. the guy who invented half the Marvel Universe and got squat for it, who was happy to help Gerber gather funds for his lawsuit. Destroyer Duck looked as awesome as he sounds.

Eclipse
Where's HIS f*****g movie? (Yes, I know I missed an opportunity for a duck pun there. f**k you.)

Anyway, Gerber and Marvel ended up settling out of court, but he wasn't entirely happy with the arrangement. Years later, Marvel asked Gerber to write a Howard/Spider-Man team up. Naturally, the man's first instinct was to tell them to polish his scrotum, but then he thought about it and hatched a little plan. Around this time, he was also writing a crossover between Destroyer Duck and Image Comics' Savage Dragon (basically a more articulate Hulk with a fin on his head), so he decided to surreptitiously link the two stories. In both issues, you see the respective heroes going into a dark warehouse and bumping into vague outlines of the other company's characters. Here's Marvel:

Marvel
But that could be any muscular character with a fin on his head.

And here's Image:

Image Comics
And, uh, lots of people have Spider-Senses, too.

What Marvel didn't know was that on Image's end of the story, you see the bad guy (classic Gerber-created Marvel villain "Elf with a gun") making hundreds of clones of Howard ... and it was actually one of those clones who left the warehouse with Spider-Man. The real Howard is saved by Destroyer Duck, dyes his feathers green, and goes into witness protection under the completely unrecognizable name "Leonard the Duck." If the big "f**k you" to Marvel wasn't clear enough, the comic ends with this new version of the cover of Howard the Duck #1:

Marvel/Image
That's Leonardverine in the background.

As far as Gerber was concerned, the Howard the Duck that Marvel owned was now a soulless clone, while the "real" Howard/Leonard continued existing at Image Comics. He even had Leonard show up in his DC Comics series Nevada -- which, while we're at it, he also "stole" from Marvel. In a 1977 Howard the Duck issue, Gerber had included a fight scene between a Las Vegas chorus girl, an ostrich, and a lamp. Nevada is entirely about ... a Las Vegas chorus girl, an ostrich, and a lamp. But I'll grant that this one could be a coincidence.

Ironically, Gerber agreed to write Marvel's version of Howard one last time, only to find out he couldn't look like the old Howard, because Disney had threatened to sue over his resemblance to Donald Duck. So Gerber turned him into a mouse.

Marvel
A Dicky Mouse. (Yes, I do puns now. f**k you.)

Howard the Duck the Mouse the Duck Again is now a Disney property after the company bought Marvel in 2009. I'm almost glad Gerber passed away in 2008, because I'm pretty sure he would have died laughing if he'd found out.

I'm not talking about Marvel creating a Flash knock-off, by the way (they already have one). It was the same guy. In 1985, the Flash had one of the most awesome deaths in or outside of comic books when he ran so fast that he dissolved into energy while destroying an antimatter cannon and saving the universes (that's plural). Here's that touching scene:

DC Comics
That's how I wanna go, too.

Writer Marv Aqua- I mean, Wolfman wrote a loophole into that scene in case they wanted to bring the Flash back via time travel, but DC never used it. Marvel, however, is another story. In a 1990 issue of Quasar (a Marvel character that I'll look silly for calling obscure when they eventually do a big movie about him, so I'll assume everyone knows him), a space god organizes a race to the moon to find out who's the fastest being on Earth. During the competition, someone materializes out of pure energy in the middle of the track:

Marvel
Or like 80 percent energy, 20 percent beard.

Despite sporting a new hobo look and having had his costume reduced to a pair of spandex shorts, that's clearly a resurrected Flash collecting his molecules after the little "running to death" incident. To make it more blatant, he later says he can't remember his name, but that it's something like "Buried Alien" -- which is like a post-autocorrect version of the Flash's secret identity, Barry Allen. Obviously, he wins the race, because even Marvel knows that DC's characters are more powerful (plus, they just stole him, so it makes no difference).

Marvel
Yes, there's a Marvel character called "The Whizzer," and yes, his costume is pee-yellow.

But this is nothing more than a friendly homage to the distinguished competition, right? Yeah, if they'd left it as a short cameo, but "Buried Alien" later showed up again with a new costume, the name Fastforward, and absolutely no desire to go back to his original universe, since he doesn't seem to be a big fan of DC's editorial practices:

Marvel
"Also, like half your superheroines have giant boobs. It's awesome."

Yeah, that's less "friendly homage" and more "taking digs at the other company through their own character." Geez, what did DC ever do to deserve such treatment, Marvel? Well ...

Wait, did I say "completely new and original" characters? Because that, ah, depends on your definition of those words. You see, while he was still at Marvel, Kirby did a series of short stories called Tales of Asgard, in which he fleshed out the Norse gods in Thor's supporting cast, as well as the magical world they lived in. Stan Lee didn't give much of a f**k at this point and let Kirby do whatever he wanted -- so Kirby killed everyone.

Marvel
"Whoa whoa, Jack! We can't say 'asunder'! This is a family comic!"

It was only a "prophecy" based on the Norse legend of Ragnarok (the final duke out between all the gods), but still, this got Kirby thinking: wouldn't it be cool to brutally murder all the characters, including Thor, and replace them with new ones? You know, like they did between Saved by the Bell and Saved by the Bell: The New Class? Kirby even included a line in his prophecy about a "young, new race of gods" that would rise from Asgard's ashes. This what they looked like:

Marvel
An era of technology, wonders, and even more ridiculous headgear than before.

In 1966, Kirby went to Stan Lee with the idea of mass killing a bunch of profitable superheroes, and Lee presumably still hasn't stopped laughing. Kirby put his "new gods" concept aside, but four years later he moved to DC and started a series called ... New Gods. Which, what do you know, opens with an epic final duke out between a race of suspiciously familiar looking characters. Check out the dude with the hammer here ...

DC Comics
That's right: It's Steel, from the 1997 Shaq motion picture, Steel.

... whose winged helmet is seen again in a later issue when one of the characters is exploring the ruins of the old, lame gods. Look familiar

DC Comics, Marvel
"Bred to violence? I'll kicketh thy face for that, thou punk-ass b***h!"

But Kirby put in another, sneakier connection between his old and new work: most readers (and future writers) assumed the planet of the New Gods existed in the DC Universe, but the only way to get there was through a "Boom Tube" -- a hole in reality that Kirby described as a "dimensional bridge." In fact, he kept referring to the New Gods as living in another dimension ... a place where Thor existed, where everyone wears ridiculous headgear, and where cosmic beings fly around using sporting goods ...

Marvel, DC Comics
If that's Silver Surfer on the left, what's the other guy called? "Black Racer"? Haha- s**t.

Yep, Jack Kirby was writing a comic set in the Marvel Universe and publishing it at DC. And he killed like 200 characters in the first issue. Just when I thought Cracked had already published the weirdest sentence about that guy, he keeps surprising us.

Maxwell Yezpitelok is in Chile, and also Twitter. Shout out to Sebas Castro, writer of the awesome webcomic Bichos Raros, for the Thor story!