The Fantastic Four: First Steps takes place on Earth-828, while the primary Avengers universe is designated as Earth-616, also known as the Sacred Timeline in the Loki series. If Earth-828 sounds familiar, that may be because it is only a single digit off from Earth-838, which was depicted as the memorable centerpiece of Doctor Strange in the Multiverse of Madness. Yet this alternate reality in First Steps is a true first for the Marvel Cinematic Universe.
Not only does the story unfold in a different dimension, the production design reflects a 1960s aesthetic. Past decades have been covered in the franchise before, with Captain America: The First Avenger staged around World War II and Captain Marvel crashing into the 1990’s. In First Steps, despite all the technological advances of Earth-828’s retro-futuristic landscape, there is not a Stark in sight.
The singular prominent genius under the spotlight in the story is Reed Richards. And the only other time Reed has shown up in the MCU, before now, was on Earth-838. In Doctor Strange in the Multiverse of Madness, Mister Fantastic was portrayed by John Krasinski. The head of the Fantastic Four is a member of the Illuminati in that universe. Unfortunately, he is pulled apart and destroyed by the Scarlet Witch.
Another Fantastic Four teammate surprisingly emerges in Deadpool & Wolverine, the first mutant-centric movie to be produced by Marvel Studios. The Human Torch tags along with the duo during their stay in the Void. Unlike Krasinski’s sole turn as Reed, Chris Evans reprises the role of Johnny Storm from the 2005 Fantastic Four and its sequel, Fantastic Four: Rise of the Silver Surfer. The in-joke about Evans playing Johnny in that MCU film is that he is most famous as the film series' fearless leader, Captain America.
Of course, the entire cast of First Steps is marking their debut as the heroic superhero family, with only slight references to any of the past iterations. The actors from the unreleased 1994 Fantastic Four cameo as a part of the montage of fans thanking the current team for their service. So other adaptations are apparently on the minds of the filmmakers. Could it merely be a coincidence that Thing picks up a crane as a weapon in the climactic battle? A powerless Ben Grimm also resorts to using a crane to swing at Doctor Doom toward the end of Fantastic Four: Rise of the Silver Surfer.
Even if all the characters in First Steps are not familiar to Earth-616, Galactus does resemble a race that is ominous in the MCU, the Celestials. Celestials were first revealed in the Collector's records in Guardians of the Galaxy and later were heavily featured in Eternals. Although Galactus is never labeled as a Celestial, he is similarly billions of years old, a giant among men, and has the power to destroy worlds.
The exclusive connection that this particular foursome has within the larger franchise was established in the previous MCU movie, Thunderbolts*. In the credits sequence, the freshly named “New Avengers” spot the Fantastic Four’s spaceship entering the atmosphere in the prime timeline.
Fans may have anticipated more on this multiversal occurrence in First Steps’ concluding moments, but instead are startled by the introduction of Doctor Doom, as another villain with his sights set on little Franklin. This is barely a glimpse of Reed Richards’ rival and the only prior hint of Doom's existence within the narrative is an empty chair held for a representative of his kingdom, Latveria.
With Doctor Doom set as the next Avenger threat, his build up to Doomsday is minimal compared to Thanos. This mid-credit scene’s closest Thanos counterpoint would be at the end of the first Avengers, when Thanos smirked without uttering a word.
From there, Thanos continued with an intimidating presence in Guardians of the Galaxy, followed by another credits cameo in Avengers: Age of Ultron; that time he spoke. Thanos' enormous spaceship was even included in the mid-credits’ stinger for Thor: Ragnarok, leading right into the plot of Avengers: Infinity War.
With Doom’s First Steps “appearance”, the famous villain is given much less escalation in advance of his big show. The only MCU movie coming out before Doomsday is Spider-Man: Brand New Day, and Spidey's solo adventure might not overlap with the fifth Avengers epic, given Tom Holland was not announced to be a part of the Doomsday cast. Even with an Avengers’ principal like Captain America, his recent feature offered limited indicators about Doomsday, although The Leader prophesizes a huge multiverse threat at the end of Captain America: Brave New World.
However, just like Thor: Ragnarok’s tease suggested Infinity War would kick-off with Thanos attacking the Asgardians, First Steps' sequence points to a very strong likelihood that Doom’s visit with Franklin Richards may be the catalyst for events to come in Avengers: Doomsday. Eventually, we should learn why the fantastic family makes the dimension hopping trek to Earth-616, as shown in Thunderbolts*.