The Avengers and Guardians of the Galaxy can't seem to catch a break.
Scattered across the cosmos, their numbers diminished and their hopes at their lowest, overcoming Thanos is all they appear to be thinking about in the trailers we've seen for Avengers: Endgame. But even if they do manage to take the Mad Titan down, what if there's yet another purple menace lurking in the cosmos, ready to consume worlds. Another of Marvel's powerful cosmic beings, Galactus could be the perfect foil to the assorted heroes of the Marvel Cinematic Universe, and while he is normally heralded himself, he could beckon change across the galaxy in his own right.
Could Galactus be the next seemingly insurmountable foe to bring the MCU to its knees?
What makes Galactus a little scarier than even Thanos is that he consumes one hundred percent of whatever world he sets his sights on. Not only that, Galactus is essentially what Thanos strives to be -- part of the balance of the universe. But where Thanos is a misguided madman with a powerful artifact, Galactus is an all-consuming being whose purpose is facilitated by the universe itself. By Endgame's end, the MCU heroes will have dealt with those who threaten the order of the universe, but how would they defy something that is an agent of it? Due to the very core of his concept, Galactus has been both a villain and an ally for the heroes of the Marvel Comics Universe, and this could also be reflected in the cinematic universe. Ultimately, however, the World-Eater always returns to his consumptive nature.
The most interesting thing about introducing Galactus to the Marvel Cinematic Universe is the potential for stories he brings. Classically a Fantastic Four villain, he could facilitate the introduction of the FF into the MCU, as the Avengers may require their help to defeat the powerful being. As the attempt to bring Galactus to the silver screen in Fantastic Four: Rise of the Silver Surfer didn't quite portray the character as fans would have liked, a fresh run at it by Marvel Studios would be welcome. Traditionally a herald to Galactus, we could even see the Silver Surfer make his MCU debut as well in a package deal.
Another argument for the appearance of Galactus in the MCU are his ties to the Skrulls. Canonically, Galactus consumed the alien race's home planet, forcing them to become the desperate and conflicting race we know them to be at times, characteristically shown in both the source material and in the most recent MCU entry, Captain Marvel. Though we are to understand the Skrulls ended up being a lot friendlier in the MCU, it may be that they haven't encountered Galactus... yet. With the alignment of Talos and his kin appearing to be on the good end of the spectrum, having Galactus consume their new home could be the straw that breaks the camel's back.
Having Galactus destroy the Skrull's new home would push the Skrulls to the level of desperation previously seen only in the source material, this would allow Marvel Studios to finally recreate Secret Invasion in the Marvel Cinematic Universe. As in the original tale, the Skrulls sought to take Earth for themselves, having nowhere else to go. Talos and his people know where Earth is, and they certainly found it to be hospitable in Captain Marvel. With the introduction of Carol Danvers and the previous introduction of T'Challa in Black Panther, we could see the formation of a team, other than the Avengers, who has links to Galactus.
The team in question is the Ultimates. Comprised of Captain Marvel, Black Panther, Spectrum, America Chavez and Blue Marvel, this group took a unique approach to removing the threat of Galactus. Using the brilliant minds of the team and their understanding of the cosmos, they managed to force evolution within the powerful entity. Accelerating his development, Galactus became a give of life, rather than a consumer, and his familiar purple color scheme turned to a more golden shade. Galactus has the potential to be an intimidating foe for the MCU after Thanos' defeat, he could also be used to facilitate introductions, stories and team formations in the MCU's future. Woe betide whoever witnesses his herald, Galactus lurks out there somewhere!