Flashpoint. Unity. Secret Invasion. Comic book fans over the years have enjoyed a variety of large sale crossover events that involved multiple superheroes and superhero teams working together to fight a much larger foe. It's a great way for your favorite heroes to work and interact together. It's also a great way to introduce readers to characters that they aren't familiar with or to comic book titles that they normally wouldn't pick up. Every year (sometimes even more frequently than that), comic book companies have big crossover events that involve characters visiting other people's comic books, but there was a time when such crossovers were not that common. That all changed with Secret Wars.

RELATED: 15 Reasons The Untitled Avengers Movie HAS To Be SECRET WARS

We're not referring to the Secret Wars that occurred in 2015 that amalgamated the Ultimate Marvel Comics Universe and the Marvel 616 Universe. That event borrowed its name from the first-ever massive crossover event that occurred in the 1980s. In Secret Wars, an all-powerful entity called the Beyonder grabbed dozens of Earth's heroes and villains and had them fight on a planet called Battleworld. The event had repercussions that echo in the Marvel Comics Universe to this very day. Did you know that Secret Wars was actually a sequel to a previous Marvel Comics event? And did you also know Deadpool was involved in the first Secret Wars? CBR invites you to take a trip down memory lane and asks how well do you know Secret Wars?

15 IT'S WHEN SPIDER-MAN GOT HIS BLACK COSTUME

Spider-Man Black Costume

If you saw Spider-Man 3 starring Tobey Maguire you saw that his black suit was an extraterrestrial symbiote. The creature came to Earth on a meteorite that crash-landed in Central Park. Although partially true, the origins of Spider-Man's black suit are much more elaborate. While on Battleworld, Spider-Man's costume was damaged and he found a machine he thought would repair his clothing.

Instead the machine produced a black ball that engulfed him and produced his infamous black costume. As fans would later find out, that black ball was actually a symbiotic alien that Peter Parker couldn't get rid of. Later, the alien would come back to haunt Spider-Man as the sometimes hero, sometimes villain named Venom. The changing of such an iconic costume was initially rejected by fans, but when Spider-Man was later able to rid himself of the symbiote, they then wanted him to keep it!

14 SECRET WARS SOLD TOYS FOR MATTEL

Mattel Toys Secret Wars

Kenner was making toys that featured the likeness of DC Comics heroes and villains. Mattel wanted to counter this by partnering with Marvel, but on the condition that the comic book company staged a publishing event that would get a massive amount of attention. Opposed to just making Marvel Comics toys, they wanted their toyline to be centered around a big, specific moment.

After collaborating with then Editor-In-Chief Jim Shooter, Mattel and Marvel came up with Secret Wars, partially due to the Mattel's thought that kids responded well to the word "secret." Scenes were written that spotlighted fortresses, vehicles and weapons that were produced as toys by Mattel. Will you ever look at your Marvel Super Heroes Secret Wars Freedom Fighter Base the same way ever again? Well played, Mattel.

13 RHODEY, NOT STARK, WAS IRON MAN

Iron Rhodey

Although Iron Man was a participant in the first Secret Wars crossover, did you know that Tony Stark was not present? At the time, the Iron Man armor was being piloted by his good friend James "Rhodey" Rhodes. Stark had a long battle with alcoholism and his problem was so severe that for a period of time he had to give up being Iron Man. Even after he was able to get his alcohol abuse under control, Rhodey still maintained his role as being the Armored Avenger.

It was during this time that Rhodey was transported by the Beyonder to Battleworld. Way before Robert Downey, Jr. uttered the phrase "I am Iron Man," the general populace thought that Iron Man was merely Stark's bodyguard, so even other heroes didn't know who Shellhead was.

12 A RETCON PLACED DEADPOOL ON BATTLEWORLD

Deadpool Retcon

Retcon is a portmanteau that stands for "retroactive continuity," where the comic rewrites history in a (hopefully) believable and surprising way. In 2015, Marvel published Deadpool's Secret Secret Wars where the Merc With a Mouth was retconned into being brought to Battleworld by the Beyonder, which is odd because Deadpool's first appearance was in New Mutants#98, released in 1991.

The comic was released during the 2015 Secret Wars event, and was used as an homage to the 1984 crossover. It also provides some added insight to famous events: in Deadpool's Secret Secret Wars #3, he first merges with the alien symbiote before Peter Parker does! When the symbiote leaves him, Deadpool hopes that merging with Wade's "twisted pysche" doesn't make the symbiote become violent and crazy. Thanks for everything, Wade!

11 THE THING GAINED THE ABILITY TO CHANGE BACK TO HUMAN FORM

Thing Becomes Human

One of the great, tragic things about The Thing is that he's a beautiful person trapped in the body of an orange rock monster. While on Battleworld, Ben Grimm found that he had the ability to transform himself back into his regular human form. Reed Richards postulated that Battleworld was somehow responsible for Grimm's newfound ability to change back and forth between his human form and his rock form.

Once the events of Secret Wars had ended, Grimm opted to stay on Battleworld and did so for a number of months. Then Ben learned that Reed lied to The Thing; it wasn't Battleworld that allowed for his transformation, it was a mental block that Grimm had placed upon himself. Oh, he also found out that his blind girlfriend Alicia Masters was cheating on him with his fellow teammate Johnny Storm. C'est la vie, Monsieur Grimm.

10 SUE STORM WASN'T THERE

Sue Storm of the Fantastic Four

Secret Wars was jam-packed with superheroes and villains. It was exciting to have artists Mike Zeck and Bob Layton draw the Avengers next to the X-Men and to The Fantastic Four! When you think of the Fantastic Four, you think a team of, well... four people. On Battleworld, only three of the four FF team members were present.

The Thing was fighting alongside Iron Man and the Hulk as well as the Human Torch. Reed Richards was there, but his wife was not to be found on Battleworld. Sue Storm was back on Earth, pregnant with their second child, Valeria. Granted, Franklin Richards would have been an excellent addition to the series, but it wouldn't be until years later that he was using his awesome powers and shaping events of the Marvel Universe.

9 IRON MAN'S GLOVES FOUGHT AN AVENGER

Marvel Comics Omnivore

Ok, let's see if we can explain this one: During Secret Wars, Iron Man's armor was modified with parts found on Battleworld. However when he returned to Earth, these components stopped functioning and Rhodey merely discarded them, thinking they were broken. The materials turned out to be sentient (similar in some degree to the "sentient" costume Spider-Man acquired on Battleworld) and they evolved into a creature named Omnivore.

The creature wound up in a place called Project Pegasus (Potential Energy Group/Alternate Sources/ United States) and fought the Avenger Quasar. Omnivore looked like a big red and silver metal bug and spat out a dissolving fluid that would allow him to consume whatever he melted. Eventually Quasar defeated it, and we wonder if this lead to any awkward conversations between Quasar and Iron Man.

8 CAPTAIN AMERICA'S SHIELD IS REPAIRED WITH HIS MIND

Secret Wars was a genre-defining moment in the 1980s that fans still talk about today. CBR wants to see how well you know the classic Marvel story.

Green Lantern's ring. Thor's hammer. These iconic items are almost as famous as the heroes that wield them. Could Captain America's shield be the most famous iconic superhero item of all time? It proudly sports the red, white, and blue of America and Captain America wields it with ease. Although nearly indestructible, his shield has actually been broken numerous times over the years and the image of Captain America's shield in pieces is both visually stunning and heartbreaking.

During Secret Wars an attack by Doctor Doom breaks Captain America's shield into pieces. At the end of the series, we see Captain America standing over his broken shield with his eyes closed and, after making a wish, the shield had mended itself! Was it due to ambient energy being present after The Beyonder took his powers back from Doom? Not a lot of explanation, but it does leave us with a breathtaking visual!

7 SPIDER-MAN'S COSTUME WAS A FAN'S IDEA

Spider-Man Fan Design

Although Secret Wars debuted in 1984, the idea for Spider-Man's black costume came to be two years earlier. Marvel ran a competition for aspiring writers and artists to submit new ideas to the Marvel Universe, and 22-year-old writer Randy Schueller proposed a black costume, only instead of a white spider, it was red. Also present was the return of the underarm webbing.

Instead of an alien symbiote, Schueller suggested it was designed in a joint venture by Reed Richard and Janet Van Dyne, built from the same unstable molecules that made up the costumes of the Fantastic Four. His web shooters would also be controlled with his mind instead of push button. Editor-In-Chief Jim Shooter purchased the idea from Schueller for $220 and tweaked its origins for Secret Wars.

6 HULK PICKED UP A MOUNTAIN

Hulk Holds Mountain

Secret Wars featured a variety of great fights between heroes and villains. One particular battle was when Owen Reece (known as the Molecule Man) used his ability to manipulate matter to take a mountain range and drop it on top of Captain America's super hero squad. So was that the last issue? What sound does Hawkeye make when he's squished by fifty billion tons of rock? Fortunately (for the reader as well as Clint Barton), the entire mountain range was caught by The Hulk!

The madder Hulk gets, the stronger the Hulk gets, so Reed Richards refers to Hulk as a dumb brute and that anger prevents everyone from being crushed! It took the combined efforts of Iron Man's armor, Spider-Man's web shooters, the energy of Captain Marvel and the Human Torch, and Reed Richards' intellect to break them free.

5 PROFESSOR X COULD WALK!

Professor Xavier Walking

Crossover events have a lot of moving parts to them. Besides the Secret Wars comic coming out, so were the independent issues that involved heroes in their own titles. In the introduction of the series, we see a beautiful splash page depicting all of the heroes staring in awe at their surroundings. One of the people who were astonished by where they are was Professor X, sitting in a wheelchair (even though in X-Men #18 Professor X walks into Beyonder's structure in Central Park).

In later issues, we see Charles walking around without much explanation. Arguably, it could have been an art error: in the X-Men comics, Charles had regained the ability to walk and artists Zeck and Layton merely could have made a continuity mistake. A possible retcon is that his walking was made possible by the Beyonder.

4 THE THING STAYED BEHIND

Ben Grimm the Thing riding a flying creature

Ben Grimm (a.k.a. The Thing) had his own comic book series called Marvel Two-In-One where The Thing would team up with another character from the Marvel Universe and go on adventures. After it was cancelled, he starred in his own book called The Thing, and although early issues showed his life as a kid on Yancy Street, a third of the series' run focused on Ben Grimm staying behind after the end of Secret Wars.

Ben was replaced by She-Hulk on the Fantastic Four and, while he was on what was left of Battleworld he got into a variety of surreal adventures, one of them was with Tarianna. They fought and The Thing later learned that she was not a real person, but rather a projection of his vision of the ideal woman. Now that's trippy, Ben.

3 MULTIPLE RETCONS OF THE BEYONDER'S ORIGINS

Beyonder Retcon

The Beyonder is from a race of omnipotent beings and are reminiscent of the Q on Star Trek: The Next Generation. No, wait, the Beyonder is not from a race of all-powerful entities, but rather he's the result of the creation of a faulty Cosmic Cube by the aforementioned Beyonders. Hold on, actually the Beyonder is really an Inhuman... well he's kind of a hybrid mutant-inhuman. I take it back. He's a Beyonder, but just a very young version from their race. Come back tomorrow and we might have a new explanation!

Writers love retconning the origins of the Beyonder that spawned the first Secret Wars in 1984. We may not know (or agree on) his ancestral origins, but every version of the Beyonder has him manipulating reality effortlessly and could arguably be one of the most powerful beings in the Marvel Multiverse.

2 KIND OF A SEQUEL TO CONTEST OF CHAMPIONS

Contest Of Champions

Marvel likes reusing its titles! The name "Secret Wars" was used in a 1984 crossover event as well as in 2015. You might be familiar with the Contest Of Champions, a video game that came out as an app in 2014, but that name was initially used in 1982. This was Marvel's first published limited series and was somewhat of a precursor to Secret Wars. Instead of the Beyonder bringing heroes and villains to Battleworld, the Elder of the Universe known as The Grandmaster, and a hooded female later to be revealed as Death, each choose about a dozen heroes and pitted them against each other.

The goal was to recover pieces of an object called "The Golden Globe of Life." You'll see Contest of Champions occur yet again in Thor: Ragnarok, as the name of the gladiatorial event that the Grandmaster is running.

1 MARVEL'S FIRST-EVER LARGE-SCALE CROSSOVER

Marvel Superheroes Crossover

Secret Wars was one of the first crossovers in comics and one of the largest. Although people often think about DC's Crisis On Infinite Earths, that came out almost a year after Secret Wars did. Crossover titles included The Amazing Spider-Man, The Avengers, Captain America, The Incredible Hulk, Iron Man, The Uncanny X-Men, Thor, The Fantastic Four, and more!

In the comics, massive changes in some of the books occurred (Spider-Man now wore a black costume, She-Hulk replaced The Thing on the Fantastic Four, etc.) in one issue, but readers had to follow the 12 issues of Secret Wars to learn what happened while the heroes were off-planet. It took between May 1984 and April 1985 for readers to learn how these changes came to be, and years later, Secret Wars is viewed as one of the best comic book events ever.

What was your favorite Secret Wars moment? Post your comments below!