Crossover is a loaded word when it comes to comic books. On the small scale, characters or teams meet up with new and unexpected allies to battle a larger threat (and often come into conflict themselves). On the bigger end, crossover events mean cosmic-level conflict that can bring in every character in a particular universe and potentially change it forever. Crossovers events are the comic book equivalent of the summer tentpole film, promising epic storytelling and a lasting impact on characters and even entire publishing lines for years to come.

Of course, with that promise also comes peril. Not every crossover lives up to the hype, leading fans (and retailers) to experience some level of "event fatigue." This malaise has become more commonplace as events in mainstream comics -- as well as reboots and relaunches -- have become increasingly more frequent. But when executed properly, there are few stories more unforgettable than a crossover.

Marvel and DC Comics have published countless crossovers over the years, some of them reaching classic status. These are the events that altered the landscape of each company's respective universe, with heroes rising and falling and universes changing for years at a time -- and in some cases forever.

8 "The Death of Superman" (1992-1993)





Writers: Dan Jurgens, Louise Simonson, Roger Stern, Jerry Ordway, Karl Kesel, William Messner-Loebs and Gerard Jones

Artists: Jon Bogdanove, Tom Grummett, Jackson Guice, Dan Jurgens, Dennis Janke, Denis Rodier, Walter Simonson, Curt Swan and M. D. Bright


The comic event no one dared imagine, "The Death of Superman" was separated into three arcs -- "Doomsday," "Funeral for a Friend" and "Reign of the Supermen!" The storyline featured the death of comics' greatest legend, the rise of four new heroes who attempted to fill the void and the stunning resurrection of the Man of Steel. It all began when new villain Doomsday -- a force of nature that cut a brutal path through the DC Universe -- did what no other villain could ever dream of and killed Superman. In addition to the story's shocking action sequences, there was great care paid to Superman's supporting casting including Jonathan and Martha Kent, Lois Lane, Jimmy Olsen, Perry White, Lex Luthor, Supergirl, seeing how Superman's loss affected each of them. Superman's death sent shockwaves through the real world and the DC Universe, and it remains one of the all-time great Superman stories.

7 "Blackest Night" (2009-2010)





Writer: Geoff Johns

Artist: Ivan Reis


What began in "Green Lantern: Rebirth" and continued in "Sinestro Corps War" ultimately culminated in "Blackest Night" when most of DC's major characters became... zombies? Geoff Johns and Ivan Reis transcended the event's gimmick to tell a story that examined the duality of life and death in the DC Universe. The DCU's living heroes battled their undead counterparts along with masters of death Nekron and Black Hand in a story so big it spilled beyond the core event series and into a number of specials and tie-ins. Despite the dark subject matter, "Blackest Night" shined a line on hope and heroism as DC's heroes bravely faced what was quite literally their darkest hour.

6 "Marvel Super Heroes Secret Wars" (1984-1985)





Writer: Jim Shooter

Artists: Mike Zeck and Bob Layton


Though initially created as a means to promote a new line of Marvel action figures from Mattel, "Secret Wars" ended up becoming a template for many crossover that followed. The premise was simple: an all-powerful being known as the Beyonder transported Marvel's biggest heroes and villains to Battleworld, a planet he created solely to watch them fight one another for his amusement. A number of heroes enjoyed new status quos, with perhaps the most famous being the debut of Spider-Man's black costume. Later revealed to be an alien symbiote, this simple "costume change" ultimately led to the birth of Venom and more than a decade of classic Spidey stories. "Secret Wars" allowed many of Marvel's legends to shine in what was the first Marvel event series, and few fans have ever forgotten moments like the Hulk lifting an entire mountain to save his friends.

5 "Flashpoint" (2011)





Writer: Geoff Johns

Artist: Andy Kubert


Many comic events claim high stakes, but few actually change everything. "Flashpoint" is the exception that proves the rule, ushering in a brand new DC Universe in its wake. But there's more than just the launch of the New 52 when it comes to "Flashpoint." The story began when Barry Allen went back in time and prevented his mother's murder. This act set off a chain reaction that created a new, alternate reality in which villains became heroes, heroes became villains and some of DC's most familiar characters took on new and shocking forms. This world's Batman was Thomas Wayne (father of the more familiar Bruce Wayne); Superman was an emaciated, frightened alien captive; Wonder Woman and Aquaman were evil despots bent on world domination. After creating the problems, the Flash was left to fix it and put the world back together. "Flashpoint" featured some of the greatest world building in crossover event history and showed a very different look at the DCU and its characters before the old DC Universe went out with a bang.

4 "Mutant Massacre" (1986)





Writers: Chris Claremont, Louise Simonson and Walter Simonson

Artists: John Romita Jr., Walter Simonson and Sal Buscema


Marvel's "Mutant Massacre" proved that a crossover event didn't have to involve every corner of the universe, it just needed to make a major impact on one of them. The ultra-violent and tragic "Mutant Massacre" saw a group of mutant hunters known as the Marauders dispatched by the newly introduced Mister Sinister to wipe out the Morlocks, a group of sewer- dwelling mutants. The Morlocks were innocents, and when the X-Men, X-Factor and the New Mutants descended into New York City's sewers to aid them an unforgettable struggle ensued, turning more than one classic X-Men character into casualties of war. In addition to the body count, "Mutant Massacre" treated fans to the very first battle between Wolverine and Sabretooth. While it didn't shake up the entire Marvel Universe, the story severely impacted the lives of many beloved characters, introduced a major new villains and left heartbroken X-Men fans begging for more.

3 "Civil War" (2006-2007)





Writer: Mark Millar

Artist: Steve McNiven


After a deadly explosion at a school in Connecticut caused by the New Warriors' pursuit of Nitro, the U.S. government drafted the Superhuman Registration Act to create oversight over Marvel's superheroes. The world's heroes sided with Captain American anti-registration or Iron Man's pro-registration, and when a compromise couldn't be made they went to war with one another. Unlike the traditional crossover event threat of some massive evil, "Civil War" took a new approach by focusing on an ideological divide instead of an enemy. When the last shot was fired, a legend was dead and the very idea of heroism was forever scarred. The series sparked intense debate amongst fans who didn't always agree with what side their favorite heroes chose, and record sales followed. Elements of the series inspired Marvel Studios' recent blockbuster, "Captain America: Civil War," and its fingerprints can be felt on the currently unfolding "Civil War II."

2 "Infinity Gauntlet" (1991)





Writer: Jim Starlin

Artists: George Perez and Ron Lim


Crossovers don't get much bigger than a First Act finale that involves half of a universe's population being wiped out. And that's why there's only one "Infinity Gauntlet." The mad Titan Thanos gained control of the realitycontrolling Infinity Gems, resulting in a desperate attempt by the remaining Marvel heroes to defeat him. In the process, almost all of them died. But that wasn't the end of the story, as "Infinity Gauntlet" ratcheted up a notch when write Jim Starlin, master of cosmic storytelling, unleashed the full, unbound fury of his imagination. The series took Thanos from niche cosmic villain to one of the greatest threats in Marvel's pantheon of evil, and its reach was seemingly limitless, with tie-ins in nearly every Marvel title published at the time. It also kicked off a trilogy of events as Starlin's "Infinity War" and Infinity Crusade" soon followed. There have been other cosmic events since "Infinity Gauntlet," but its consequences defined the cosmic side of Marvel for decades and none have come close to taking the crown.

1 "Crisis on Infinite Earths" (1985-1986)





Writer: Marv Wolfman

Artist: George Perez


There's never been a crossover bigger than "Crisis on Infinite Earths." Designed to celebrate 50 years of DC publishing history, it also created a brand new continuity for the next phase of the DC Universe. If that sounds ambitious, you're right -- but where some events seem hesitant to actually leave a mark on their respective universes, "Crisis" did it with aplomb. Everything fans loved about the DC Universe was contained in the 12-issue event, as Golden Age characters fought side by side with modern day heroes while reality literally came crashing down around them. Not only did the story feature the costumed heroes of the DCU, it also paid tribute to the publisher's horror, western, sci-fi and fantasy characters, as Wolfman and Perez explored every corner of DC Comics' rich history. Of course, with a title like "Crisis," you'd expect some major occurrences; while each issue featured some shocking moment, none were as unbelievable as the deaths of Supergirl and the Flash (Barry Allen). When the dust finally settled, the multiverse was no more, a single, concise DC Universe standing in its place, designed to welcome new readers, reinvigorate characters and make everything old new again.

What's your favorite crossover? Let us know in the comments!