Galactus' defeat inThe Fantastic Four: First Stepswill actually makeAvengers: Doomsday’s Doctor Doom more threatening. Galactus was just one of manyvillains inThe Fantastic Four: First Steps, but he was by far the most deadly. Galactus threatened to destroy the Earth, all while trying to get his hands on Franklin Richards.
InFantastic Four: First Steps' ending, however, the titular team defeated him by teleporting him across the universe without his ship. This led to peace on Earth-828 once more, beforeThe Fantastic Four: First Steps' post-credit sceneteased Doctor Doom’s arrival. Of course, this teasesAvengers: Doomsday’s story.

Many assumed that the actual story ofFantastic Four: First Stepsitself, not just the post-credit scene, would teaseDoomsday, but this proved not to be the case. That said, Galactus' defeat and the motivation for it on The Fantastic Four’s part may make Doom more dangerous come the release ofAvengers: Doomsdayin December 2026.
Galactus' Defeat Proved How Far The Fantastic Four Would Go To Protect Earth-828
828’s Citizens Are Family To The Four
ThroughoutThe Fantastic Four: First Steps, the titular team came up with several different plans to defeat Galactus. This involved teleporters, bringing the world together for resources and the conservation of energy, and the final battle on the streets of New York with the planet-devouring giant. This allowed for a lot of great moments inFantastic Four: First Steps.
More than just great moments were gleaned from this, however, with these seemingly endless plans proving how far The Fantastic Four would go to protect Earth-828. A big theme of this movie was family, though this was not solely limited to the familial links between the team.

Midway through the movie,Sue makes a speech that implies the people of their universe are her family, too. She states that she, Reed, Ben, and Johnny will always protect the people of Earth, capitalizing on the goodwill shown between the team and 828’s civilians in the film’s opening montage. Clearly, 828 is incredibly important to The Fantastic Four.
Doom Threatening The Multiverse In Avengers: Doomsday Makes Him More Deadly To Earth-828
Explaining The Fantastic Four’s Involvement
As alluded to, Doctor Doom will be the villain ofAvengers: Doomsday.If the writers of the film opt to make him a straight-up villain who threatens the multiverse in some way, just as Kang the Conqueror was, then Earth-828 will also be in the firing line. This gives The Fantastic Four an excellent reason for teaming up with The Avengers and the X-Men against Doom.
Doom’s plans for Franklin Richards will likely also serve as motivation for The Fantastic Four inAvengers: Doomsday.
Although it is unclear exactly what Doctor Doom wishes to achieve inAvengers: Doomsday, the character usually has a rivalry with The Fantastic Four. If that continues in the film, it would make sense for him to threaten Earth-828. This will not only feel more consequential afterFantastic Four: First Steps,but it will increase Doom’s threat.
This possibility makes more sense if the MCU opts to simply replace Kang with Doom, but keep the same story. Kang was set on conquering the multiverse using his variants, with Doom possibly looking to do the same. If so, it would make sense for Doom to threaten Earth-828.
AfterThe Fantastic Four: First Steps, it would be logical for the titular team to oppose this in any way they possibly can, just as they did with Galactus.
Avengers: Doomsday Making Doom The “Hero” Still Makes Him Dangerous To The MCU Multiverse
Another possibility forAvengers: Doomsdayis that the film portrays Doom as a “hero,” in the sense that he thinks what he is doing is right. Given that the film will lead intoAvengers: Secret Wars, this is not out of the realm of possibility.
The 2015Secret Warscomic book run had Doom teaming up with Doctor Strange and the Molecule Man to stop incursions across the multiverse. Doom was too late, though, and eventually used the Molecule Man’s power to save what was left and create Battleworld. IfAvengers: Secret Warsfollows this story,Doomsdaycould focus on Doom’s attempts to stop incursions.
If Doctor Doom is the variant from Earth-828, teased inThe Fantastic Four: First Steps’Latveria reference, it would make sense for him to be trying to save that world from an incursion. However, this would still make him more deadly, as he could selfishly abandon other universes to their, well, dooms.
Beyond making Doom more deadly in this way, it would also provide strong motivation for the X-Men and Avengers to get involved. These universes could be two that are threatened with incursions somehow, yet Doom - likely with the power to stop them - may only be focused on Earth-828.
Doom clearly needs Franklin for something, meaning he would want to keep 828 alive…
Even if Doom is not from 828, he could wish to save that universe because ofThe Fantastic Four: First Steps’post-credit scene. Doom clearly needs Franklin for something, meaning he would want to keep 828 alive, no matter the cost to other universes.
In either scenario, Doom will be made much more threatening. This stems from Galactus' defeat inThe Fantastic Four: First Steps,thanks to how that film made Earth-828 feel so important. As a result,Avengers: Doomsdaywill feature a villain more deadly than first thought.