The end of the Marvel Cinematic Universe’s Phase Three is upon us, but Marvel Studios is keeping their knowledge of what’s next for the MCU close to the vest. With little information to go on, dedicated Marvelites have been forced to wildly speculate about who the antagonists of Phase Four will be - and given the lengthy history of the villainous Skrulls in Marvel Comics, they’re probably the best bet.
The Skrulls are a shapeshifting race of aliens that have been a part of Marvel Comics continuity since 1962, when they first clashed with the Fantastic Four. They’re the primary antagonists in 2019’s Captain Marvel, where they’ll make their cinematic debut - but many expect that it won’t be their last appearance. The Skrull Empire is notorious for playing the “long game” - most notably during their Secret Invasion of the Marvel Universe - so it’s safe to say that they’re a threat that won’t be going away anytime soon.
Like most comic book events, Secret Invasion took place within a calendar year of publishing, but it’s in-universe origins stretch back years into the past. As the depths of the infiltration are slowly revealed throughout the event, the heroes of Earth soon realize that the Skrull Empire’s plan - which involves kidnapping and replacing various influential Earthlings via their shapeshifting abilities and then taking control of the world from within - has been in the works for an extraordinarily long time.
Over decades of comic book storylines, the Skrulls have taken a series of beatings at the hands of the Avengers, the Kree Empire, and various other cosmic beings, and all that losing provides the impetus for their invasion and their forceful acquisition of Earth as their new homeworld.
Most comic book villains announce their evil intentions via an expository monologue, but the Skrull’s Secret Invasion is revealed in a much more dramatic fashion. During a routine mission against the Hand in Japan, Echo of the New Avengers fatally stabs Elektra Natchios - only to watch her corpse transform into a green alien.
This incident wakes the big brains of the Marvel Universe - individuals like Tony Stark and Reed Richards - to the fact that the Skrulls are once again attempting to invade Earth, and that they’ve developed methods to avoid detection. Suddenly, the Avengers and their allies must accept that anyone could theoretically be a Skrull in disguise - and it becomes a dangerous game of “Who Do You Trust?”
The Skrulls have a multitude of reasons to secretly invade the Earth. The most direct inciting incident comes during the events of Annihilation, in which their homeworld of Tarnax IV is consumed by Galactus, scattering the once-proud Skrull Empire across the universe and fracturing their political structure.
Like many real-world conflicts, however, the Secret Invasion also has a major religious component. An obscure prophecy from a Skrull religious text claims that the Skrulls are destined to one day occupy the Earth as their permanent homeworld, and that doing so is in the best interest of the original inhabitants. That’s why the Skrulls constantly refer to their god as they take over the planet, creepily informing the Earthlings that “He loves you.”
There’s also a significant “prideful revenge” component to the Skrull’s Secret Invasion. The smartest individuals of the Marvel Universe - Reed Richards, Tony Stark, Charles Xavier, Stephen Strange, and the like - had formed an “Illuminati” that they hoped would be able to address future threats before they occurred. Unfortunately, they fell victim to their own hubris.
During one mission, the Illuminati travel to Tarnax IV before its destruction and proactively inform the Skrull Empire that they’ll destroy them if they ever attack Earth again. After Tarnax IV is consumed by Galactus, the Skrulls find themselves no longer able to ignore this slight, and so they set about showing the Illuminati the errors of their arrogance.