Anyway, after many theories, and fake Multiverse, the Marvel Multiverse in theaters will come true. But who is largely responsible for literally opening the doors of the Multiverse? Which of the MCU Phase 4 characters made this possible, or none of them?
Finally fans can celebrate with all the certainty that exists in this world, the Marvel Multiverse in theaters is official and it's coming. It is not possible that they will deceive us twice in a row, that would be digging their own grave. So much the Doctor Strange movie already bears the Multiverse title, the God of Lies Loki series took the theme even further, and now we have the Spider-Man trailer making his existence clear.
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Who “created” the Marvel Multiverse in the MCU?
But the question remains, who was largely responsible for creating the Multiverse on the big screen? He has been approached so far in 2 places with possible origins, in the Loki series, and in the Spider-Man No Return Home trailer. But it is possible that another character has responsibility, Wanda (Scarlet Witch) in the WandaVision series.
Let's list in the order presented in the movies and series the possible responsible for the "creation" of the MCU Multiverse.
Wanda Maximoff (Series – WandaVision)

Much was expected during the WandaVision series that Wanda would open the multiverse, after all, it is known that she will be important in the next Dr. Stranger in the Multiverse of Madness. But the series ended up focusing on Wanda dealing with her trauma.
The important thing comes at the end of the series, where she discovers what she really is, a being "nexus“, able to transit between universes. And that she would have destabilized the Multiverse by discovering her powers and transforming into Scarlet Witch. In addition to his study of the book of the Damned.
Loki and Sylvie (Series – Loki)

In “Loki”, one of the MCU series on Disney+, we discover the existence of an organization called AVT that is responsible for literally exterminating events that give rise to ramifications in the timeline, which would give rise to new realities until the emergence of a Multiverse.
The Multiverse once existed, but we discover that a being behind the creation of the AVT is responsible for creating a single timeline in order to end a Multiversal War. Loki, along with a variant of him who took the name Sylvie, meet this being, who we discover to be a version of Loki. kang.
When confronting him, they discover the whole story behind the creation of the AVT, etc. But Sylvie is determined to kill him for all the suffering she's already suffered, and to instill "free will" in the universe. The moment she kills him, we see the timeline branch out wildly.
Doctor Strange (Movie - Spider-Man: No Homecoming)

Finally we have, albeit with few details, the supreme mage. Few details, after all, we only see this scene for a few moments, in just one trailer, which by the way is the first of the film, which reveals less details of the plot.
In it we see Doctor Strange doing a spell to help Peter Parker who had his secret identity revealed by the villain Mysterio (including the first to mention the Multiverse in the Marvel movies, albeit on a bluff). After something goes wrong with your spell, we see reality “splinter” for a few moments.
In the course we see old villains of Spider-Man, from films starring Tobey Maguire Andrew Garfield, which gives us two hypotheses:
- The “mistake” in the spell shattered the sacred timeline, causing ramifications.
- The "mistake" somehow brought Spider-Man-related characters from other realities, even Tom Holland's. In this case, the Multiverse would already be open.
What if whoever opened the Marvel Multiverse is…
Both are strong candidates to have created the Marvel Multiverse, but there is another option, which makes a lot of sense, but obviously it's just a theory. Keen fans noticed that the events of WandaVision and Loki happen at exactly the same time throughout the episode. Which could also happen with the Spider-Man movie.
In other words, a very strong theory says that it was not just one of them that opened the multiverse of Marvel movies, but the action of the 3, at exactly the same moment. Which makes a lot of sense, if you look closely, in Loki, we hear thunder just as Kang says he doesn't know what's going to happen after that moment. This thunder also happens in WandaVision when Wanda awakens her powers.
And if you look closely, you'll notice that the sacred timeline starts branching out before Kang is killed by Sylvie. Not to mention there's no way the most powerful Sorcerer in all of Marvel could miss a spell just because Peter Parker talked to him. It could be that the events of Loki and Wanda influenced their spell. That or someone sabotaged it...
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