The lore of theMarvel Universeis vast and complex, but there’s one jaw-dropping secret that dwarfs all the others, answering some of fans' biggest questions about the beloved interconnected universe. While heroes like Spider-Man, the Avengers, the Fantastic Four and the X-Men may have their own origin stories, it turns out thatevery single one of them was created to battle against the same threat: the Death Celestials.
The Death Celestials are cosmic predators who travel the multiverse terrorizing and destroying one reality after another. On some worlds, superpowered heroes have opposed them, but always unsuccessfully.Marvel’s mainstream reality was created to finally stop the Death Celestials- a reality where superhumans are far more common than anywhere else, creating an unknowing army in preparation for the day the Death Celestials arrive.

This huge piece of lore was revealed in 2012’sDefenders, from Matt Fraction, Terry Dodson, Michael Lark, Jamie McKelvie and more. A lesser-known series,Defendersended abruptly, but the cosmic lore it introduced has since been supported by series including 2015’sUltimates(Al Ewing, Kenneth Rocafort) and the recentDefenders: Beyond(Al Ewing, Javier Rodríguez.)
Superheroes are the foot soldiers in a battle that goes right to the top of Marvel’s cosmic powers.

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The Avengers, X-Men and More Were All Created to Face the Death Celestials
Marvel’s Superheroes Are a Cosmic Defense Mechanism
InDefenders, the titular team (led by Doctor Strange) encounter a device called a Concordance Engine (which first appeared in 1966’sFantastic Four #54, from Stan Lee and Jack Kirby.) It’s eventually revealed that the engines were created by a group of heroes who escaped a reality destroyed by the Death Celestials, designed as a long-term weapon against them.
The Death Celestials are cosmic gods whichworship and serve the First Firmament, who we’ll come to shortly. Driven by cruelty, boredom, and the desire to remove variety and change from the multiverse, they journey to reality after reality, obliterating each from existence. InDefenders #10, Scott Lang’s Ant-Man reveals that theDeath Celestials are beyond any villain the Avengers have ever fought, since destructive power is inherent to their nature. He explains:

It’s like it can eliminate thought. It can decide – today I’m done with cats. And all the cats were gone. There wasn’t any fighting. Things that were… suddenly were not.
Against such powerful beings, an unfathomable army is needed to stand a chance, which is where the Concordance Engines come in.

Concordance Engines are the key to every superhero origin in Marvel lore.
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Marvel’s Concordance Engines Answer Every Huge Lore Question
Everything from Why Supeheroes Exist to Why Earth Is So Important
Defendersreveals that in one reality, a group of heroes managed to escape (but not defeat) the Death Celestials. These heroes made it their mission to try and stop the villains, searching the multiverse for unique beings who could stand against them. They then created theConcordance Engines, which sense the creation of a unique superhuman anywhere in the multiverse, then recreate their origin in Marvel’s mainstream universe, aka Earth-616.
This explains why so many superheroes have miraculous origins.Defendersshows that on countless worlds, people like the Fantastic Four were bombarded with cosmic rays, dying in the process. However, once the Concordance Engines found theonereality where they gained powers, it then recreated those conditions on Earth-616, doing the same with everyone from the Incredible Hulk to Spider-Man.This explains why Marvel’s reality has so many heroes, all gaining their powers from different sources.

Another dangling thread in Marvel lore iswhy Earth is so central to galactic events. Despite being a planet in its relative infancy, Earth is the home to the Sorcerer Supreme, is the favorite stomping ground of various gods, and has offered upmultiple Phoenix Force hosts. This is revealed to be because Earth is the site of the Concordance Engines.
The Concordance Engines connects the Beyonders, Celestials and even the King in Black.

Another fun detail of this reveal is that it explains why Marvel has so many characters who seemingly reference other works. Heroes like Hyperion and Nighthawk are obvious references to DC Comics' Superman and Batman, the American Kaiju is a clear reference to Godzilla, andSherlock Holmes was actually X-Men’s Mystiquein disguise.The Concordance Engines would explain why characters from other realities reliably manifest on Earth-616.
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The War Between the First Firmament & Celestials Is Core to Marvel Lore
Marvel’s Ultimate Villain Is Responsible for So Much Cosmic Lore
Defendersdoesn’t dig into the Death Celestials' motivations beyond cruelty and boredom, butUltimatesandDefenders: Beyondexplain the stakes and players at the highest level of Marvel lore.Ultimatesreveals the existence ofthe villainous First Firmament- the embodiment of the very first version of Marvel’s multiverse. The First Firmament created the cosmic race of Celestials, who spent all their time in constant worship of their creator. However,a rogue group of Celestials broke free, wanting to introduce choice and change into reality.
Thus began a cycle that has created multiple versions of the multiverse, with Marvel’s current Earth-616 existing in the eighth cycle. However, the First Firmament still exists, and is consumed with jealousy and hatred, wanting to absorb all other aspects of reality to once again become all that exists. The Death Celestials (also known as the Aspirants) are the loyal servants of the First Firmament, while the rogue Celestials are the colorful version fans know.

The Death Celestials are opposed by the regular, colorful Celestials that Marvel fans are more familiar with.These Celestials tend to the multiverse, encouraging as many different kinds of life as possible to grow and thrive - partly to provide an army against their creator. To this endthey created the Beyonders, who work towards their ends from outside reality, and the King in Black, who is supposed to work from within. It’s the Beyonders who operate the Concordance Engines, under the name of the Omega Council.
While the originalKing in Black became a huge threatin the Marvel Universe, this was only because he refused to follow the Celestials' plan.
Marvel’s Entire Multiverse Is a Gigantic Cosmic Battleground
The Avengers, X-Men and Fantastic Four Are Pawns in a Grand Conflict
This may all seem like a lot to take in, but remember thatit explains the origin of the entire Marvel multiverse and every supehero in existence, as a jealous god tries to reclaim a multiverse that has grown beyond its control.
There’s a lot more to this conflict - every cycle of the cosmos has its own embodiment similar to the First Firmament, who he considers his primary enemies - but the First Firmament, Death Celestials, and Concordance Engines explain the conflict at the heart ofMarvellore, and why Earth is home to so many different forms of superhuman life.