MCU: 10 Insanely-Powerful Villains Who Could Be The New Thanos
3. Galactus
One of the biggest benefits of having the Fantastic Four back is the fact that this means we also have all of the weird as hell cosmic stuff associated with them back as well. Including the one that started it all: Galactus, Devourer Of Worlds.
The guy is exactly what his title promises, he's a godlike being who wanders the universe looking for worlds to devour. Not out of any malice, the thing likely isn't even capable of holding a slight grudge against something as small in comparison to his majesty as a human. It's just that he's hungry - insatiably so - and what he eats are the various minerals and materials that just so happen to make habitable planets.
Seeing him show up in the MCU would be interesting because unlike Thanos - he's not doing this out of some insane dogma - he's doing this because he's hungry. And thus can be potentially convinced to leave or driven off by making Earth just not worth the trouble. However, while Thanos wanted to become a god, Galactus is one. So fighting him would likely be seen by the heroes as a last resort.