Secret Wars was a universe-wide crossover event in the comics. And when you ask Google who is the most powerful villain in all of Marvel, you’ll get the one featured in this story. There’s enough reason to see why Marvel execs would want the end of the multiverse saga to end with Secret Wars. It showcases literally every one of Marvel's most powerful heroes and villains, with the added benefit of the story coming literally out of nowhere. Marvel won’t have to do any kind of setup or worry about connecting any dots before debuting Secret Wars. All it has to do is have a lot of movies with a lot of heroes.
The villain in Secret Wars isn’t one that plots for years, carefully moving pieces like a chess match until it’s his time to strike. He isn’t one that waits for a series of events to line up in a certain way before he can move. He doesn’t need resources, weapons, allies, or abilities, because, in a manner of speaking, he already has them. This villain was made to be supreme, imagined to be the most powerful thing the human mind can conceive of. He is an entire universe. He is Beyonder.
Beyonder Discovers the Multiverse
In the comics, the concept of Secret Wars is fairly easy to describe: a group of superheroes and supervillains are teleported to another world and forced to do battle with each other. The war is secret because all of this happens without any consequence or recognition. And the planet is called Battleworld because, well, you can figure that one out.
This story is particularly suited to something the MCU is calling the multiverse saga because Beyonder is essentially another universe in one being. Before appearing, Beyonder existed in a dimension separate from the multiverse and was a lone entity making up the entirety of his reality. He was pulled into the multiverse by a tachyon beam that a group of supervillains called Intel were using to try and attract a vibranium meteor.
Although Secret Wars is more or less a tangential storyline that doesn’t really affect the overall Marvel Universe until the rest of the Beyonder race comes in, some villains in the group Intel are being introduced to the MCU in the future phases, including MODOK and Doom.
When Beyonder was brought into existence in the multiverse, he noticed that each sentient being was a creation unto itself. He was amazed at the multiplicity of this reality because where he existed, he was everything that existed. The idea that sentience could exist in multiple different people, or that more than one thing could exist at all, astounded him. But as Beyonder observed that each thing here existed as part of a larger thing called a universe, and that universe was only a part of a great collection of universes called a multiverse. That idea of parts making up a whole meant to Beyonder that everything in this existence was inherently incomplete. This incompleteness created desire since everything shared with everything else the desire to become whole due to the fact that they were inherently not.
So as Beyonder observed incomplete things struggle to become complete, he realized that he, too, was incomplete since he previously thought that he was all that existed. Now, with the realization that he was not everything in all of reality, he felt desire and thus began to question it by experimenting.
Beyonder Sends Heroes and Villains to Battle in Secret Wars
In order to understand the nature of desire, Beyonder teleported a great number of heroes from the Avengers, X-Men, and Fantastic Four, as well as many villains, including, among others, Kang, Ultron, and Galactus, to a world far outside the galaxy in which Earth existed, dubbed Battleworld.
There, Beyonder separated the factions of heroes and villains and told them, "I am from beyond! Slay your enemies, and all you desire shall be yours! Nothing you dream of is impossible for me to accomplish!" Thus causing many of the villains to selfishly pursue destroying their respective heroes and forcing the heroes to defend themselves. All done for the desire of Beyonder’s promised prize.
While Charles Xavier and Reed Richards were working on a peaceful solution to their predicament, it was Doctor Doom who “won” the Secret Wars. Using a strange bit of technology, Doom created a machine that could steal the Beyonder’s power. With the immense amount of energy coursing through Doom’s body, the Beyonder was not strong enough to punish him. So instead, he possessed a villain named Klaw and began stealthily manipulating Doom, planting a seed of doubt in his mind that he didn’t have the ability to control such power.
Eventually, Beyonder (inside Klaw’s body) convinced Doom to transfer some of that power to him. With a portion of his strength returned, Beyonder left Klaw’s body, and all the participants of the Secret Wars were instantly teleported back to where they came from.